NMT – a new individual ion counting method: comparison to a Faraday cup Chem. Phys. (IF 1.767) Pub Date : 2018-01-17 Michael Burton, Boris Gorbunov
Two sample detectors used to analyze the emission from Gas Chromatography (GC) columns are the Flame Ionization Detector (FID) and the Electron Capture Detector (ECD). Both of these detectors involve ionization of the sample molecules and then measuring electric current in the gas using a Faraday cup. In this paper a newly discovered method of ion counting, Nanotechnology Molecular Tagging (NMT) is tested as a replacement to the Faraday cup in GCs. In this method the effective physical volume of individual molecules is enlarged up to 1 billion times enabling them to be detected by an optical particle counter. It was found that the sensitivity of NMT was considerably greater than the Faraday cup. The background in the NMT was circa 200 ions per cm3, corresponding to an extremely low electric current ∼10-17 A.
Molecular Mechanism of Melting of a Helical Polymer Crystal: Role of Conformational Order, Packing and Mobility of Polymers Chem. Phys. (IF 1.767) Pub Date : 2018-01-13 Ramesh Cheerla, Marimuthu Krishnan
NO3 full-dimensional potential energy surfaces and ground state vibrational levels revisited Chem. Phys. (IF 1.767) Pub Date : 2018-01-12 Alexandra Viel, Wolfgang Eisfeld
A new full-dimensional (6D) diabatic potential energy surface (PES) model is presented representing the five lowest PESs corresponding to the X ̃ 2 A 2 ′ , A ̃ 2E′′ 2 E ′ ′ , and B ̃ 2E′ 2 E ′ electronic states of the nitrate radical (NO3). It is based on high-level ab initio calculations of roughly 90 000 energy data over a wide range of nuclear configurations and represents the energies with a root mean-squares (rms) error of about 100 cm-1 cm - 1 . An accurate dipole surface was developed for the X ̃ state as well. The new PES model is used to re-investigate the infra-red (IR) spectrum corresponding to the electronic ground state by full quantum dynamics simulations. Vibrational eigenstates, IR transition probabilities, and isotopic shifts are computed and analyzed. Levels up to 2000 cm-1 cm - 1 are obtained and show good to excellent agreement with known experimental values. Some larger deviations are observed and discussed as well. The new results are in agreement with previous theoretical studies that the disputed ν3 ν 3 fundamental corresponds to a frequency of roughly 1022 cm-1 cm - 1 and that the prominent experimental feature observed at 1492 cm-1 cm - 1 is due to the 3141 3 1 4 1 (e′ e ′ ) combination mode. Observed discrepancies in the IR intensities may be explained by coupling to the B ̃ state which is also analysed by diabatic decomposition of the eigenstates.
Possible influence of the Kuramoto length in a photo-catalytic water splitting reaction revealed by Poisson–Nernst–Planck equations involving ionization in a weak electrolyte Chem. Phys. (IF 1.767) Pub Date : 2018-01-10 Yohichi Suzuki, Kazuhiko Seki
Angle Dependence in Slow Photon Photocatalysis using TiO2 Inverse Opals Chem. Phys. (IF 1.767) Pub Date : 2018-01-10 Mariano Curti, Gonzalo Zvitco, María Alejandra Grela, Cecilia B. Mendive
Exploration for the stabilities of CHN7 and CN7-: A theoretical study on the formation and dissociation mechanisms Chem. Phys. (IF 1.767) Pub Date : 2018-01-10 Tao Yu, Ying-Zhe Liu, Wei-Peng Lai
Direct Application of the Phase Estimation Algorithm to Find the Eigenvalues of the Hamiltonians Chem. Phys. (IF 1.767) Pub Date : 2018-01-04 Ammar Daskin, Sabre Kais
The eigenvalue of a Hamiltonian, H H , can be estimated through the phase estimation algorithm given the matrix exponential of the Hamiltonian, exp(-iH) exp ( - i H ) . The difficulty of this exponentiation impedes the applications of the phase estimation algorithm particularly when H H is composed of non-commuting terms. In this paper, we present a method to use the Hamiltonian matrix directly in the phase estimation algorithm by using an ancilla based framework: In this framework, we also show how to find the power of the Hamiltonian matrix-which is necessary in the phase estimation algorithm-through the successive applications. This may eliminate the necessity of matrix exponential for the phase estimation algorithm and therefore provide an efficient way to estimate the eigenvalues of particular Hamiltonians. The classical and quantum algorithmic complexities of the framework are analyzed for the Hamiltonians which can be written as a sum of simple unitary matrices and shown that a Hamiltonian of order 2n 2 n written as a sum of L number of simple terms can be used in the phase estimation algorithm with (n+1+logL) ( n + 1 + logL ) number of qubits and O(2anL) O ( 2 a nL ) number of quantum operations, where a is the number of iterations in the phase estimation. In addition, we use the Hamiltonian of the hydrogen molecule as an example system and present the simulation results for finding its ground state energy.
Magnetic modulation of the unbraiding dynamics of pairs of DNA molecules to model the system as an intermittent oscillator Chem. Phys. (IF 1.767) Pub Date : 2018-01-04 Carlos J. Martínez-Santiago, Edwin Quiñones
iCorrelation between the size and the magnetic properties of Ag2+ clusters loaded on ceria surface and their catalytic performance in the total oxidation of propylene. EPR study. Chem. Phys. (IF 1.767) Pub Date : 2018-01-03 Sara Hany, Mira Skaf, Samer Aouad, Cédric Gennequin, Madona Labaki, Edmond Abi-Aad, Antoine Aboukaïs
A Molecular Electron Density Theory study of the chemo- and regioselective [3+2] cycloaddition reactions between trifluoroacetonitrile N-oxide and thioketones Chem. Phys. (IF 1.767) Pub Date : 2018-01-02 Saeedreza Emamian, Tian Lu, Luis. R. Domingo, Leily Heidarpoor Saremi, Mar Ríos-Gutiérrez
Collective effect of light-induced and natural nonadiabatic phenomena in the dissociation dynamics of the NaI molecule Chem. Phys. (IF 1.767) Pub Date : 2018-01-02 András Csehi, Gábor J. Halász, Ágnes Vibók
Natural and light-induced nonadiabatic effects are ubiquitous in many photochemical and photophysical processes. Here we study the interplay between them when they are present simultaneously in a molecular system. Our showcase example is the NaI NaI molecule. Solving the time-dependent nuclear Schrödinger equation the photodissociation rate and the angular distribution of the molecular photofragments are calculated and discussed at several resonant laser energies and intensities. Obtained results clearly demonstrate that the dissociation rate and the angular distribution of the NaI NaI photofragments can be considered as clear fingerprint of a collective effect of light-induced and natural nonadiabatic phenomena.
Stretched-to-compressed-exponential crossover observed in the electrical degradation kinetics of some spinel-metallic screen-printed structures Chem. Phys. (IF 1.767) Pub Date : 2018-01-02 V. Balitska, O. Shpotyuk, M. Brunner, I. Hadzaman
Thermally-induced (170°C) degradation-relaxation kinetics is examined in screen-printed structures composed of spinel Cu0.1Ni0.1Co1.6Mn1.2O4 ceramics with conductive Ag or Ag-Pd layered electrodes. Structural inhomogeneities due to Ag and Ag-Pd diffusants in spinel phase environment play a decisive role in non-exponential kinetics of negative relative resistance drift. If Ag migration in spinel is inhibited by Pd addition due to Ag-Pd alloy, the kinetics attains stretched exponential behaviour with ∼0.58 exponent, typical for one-stage diffusion in structurally-dispersive media. Under deep Ag penetration into spinel ceramics, as for thick films with Ag-layered electrodes, the degradation kinetics drastically changes, attaining features of two-step diffusing process governed by compressed-exponential dependence with power index of ∼1.68. Crossover from stretched- to compressed-exponential kinetics in spinel-metallic structures is mapped on free energy landscape of non-barrier multi-well system under strong perturbation from equilibrium, showing transition with a character downhill scenario resulting in faster than exponential decaying.
Direct observation of the change in transient molecular structure of 9,9'-bianthryl using a 10 fs pulse UV laser Chem. Phys. (IF 1.767) Pub Date : 2017-12-28 Sena Hashimoto, Atsushi Yabushita, Takayoshi Kobayashi, Kotaro Okamura, Izumi Iwakura
Anharmonic Vibrational Spectroscopy Calculations Using the Ab Initio CSP Method: Applications to H2CO3, (H2CO3)2, H2CO3-H2O and Isotopologues Chem. Phys. (IF 1.767) Pub Date : 2017-12-26 Lior Sagiv, Barak Hirshberg, R. Benny Gerber
Photochemical Dynamics of a Trimethyl-Phosphine Derivatized [FeFe]-Hydrogenase Model Compound Chem. Phys. (IF 1.767) Pub Date : 2017-12-23 Rachel L. Meyer, Annette D. Zhandosova, Tara M. Biser, Edwin J. Heilweil, Christopher J. Stromberg
Though there have been many studies on photosensitizers coupled to model complexes of the [FeFe]-hydrogenases, few have looked at how the models react upon exposure to light. To extract photoreaction information, ultrafast time-resolved UV/visible pump, IR probe spectroscopy was performed on Fe2(μ-S2C2H4)(CO)4(PMe3)2 (2b) dissolved in heptane and acetonitrile and the photochemical dynamics were determined. Excitation with 532 and 355 nm light produces bleaches and new absorptions that decay to half their original intensity with time constants of 300 ± 120 ps and 380 ± 210 ps in heptane and acetonitrile, respectively. These features persist to the microsecond timescale. The dynamics of 2b are assigned to formation of an initial set of photoproducts, which were a mixture of excited-state tricarbonyl isomers. These isomers decay into another set of long-lived photoproducts in which approximately half the excited-state tricarbonyl isomers recombine with CO to form another complex mixture of tricarbonyl and tetracarbonyl isomers.
CO Oxidation on Al-Au Nano-composite Systems Chem. Phys. (IF 1.767) Pub Date : 2017-12-23 Chinagandham Rajesh, Chiranjib Majumder
Using first principles method we report the CO oxidation behaviour of Al-Au nano-composites in three different size ranges: Al6Au8, Al13Au42 and a periodic slab of Al-Au(111) surface. The clusters prefer enclosed structures with alternating arrangement of Al and Au atoms, maximising Auδ--Alδ+ bonds. Charge distribution analysis suggests the charge transfer from Al to Au atoms, corroborated by the red shift in the density of states spectrum. Further, CO oxidation on these nano-composite systems was investigated through both Eley -Rideal and Langmuir Hinshelwood mechanism. While, these clusters interact with O2 non-dissociatively with an elongation of the O-O bond, further interaction with CO led to formation of CO2 spontaneously. On contrary, the CO2 evolution by co-adsorption of O2 and CO molecules has a transition state barrier. On the basis of the results it is inferred that nano-composite material of Al-Au shows significant promise toward effective oxidative catalysis
Reaction Mechanism and Kinetics of the Degradation of Terbacil initiated by OH radical - A Theoretical Study Chem. Phys. (IF 1.767) Pub Date : 2017-12-22 S. Ponnusamy, L. Sandhiya, K. Senthilkumar
The reaction of terbacil with OH radical is studied by using electronic structure calculations. The reaction of terbacil with OH radical is found to proceed by H-atom abstraction, Cl-atom abstraction and OH addition reactions.The initially formed alkyl radical will undergo atmospheric transformation in the presence of molecular oxygen leading to the formation of peroxy radical. The reaction of peroxy radical with other atmospheric oxidants, such as HO2 and NO radicals is studied. The rate constant is calculated for the H-atom abstraction reactions over the temperature range of 200 to 1000 K. The results obtained from electronic structure calculations and kinetic study show that the H-atom abstraction reaction is more favorable. The calculated lifetime of terbacil is 24 hours in normal atmospheric OH concentration. The rate constant calculated for H-atom abstraction reactions is 6x10-12, 4.4x10-12 and 3.2x10-12 cm3molecule-1s-1, respectively which is in agreement with the previous literature value of 1.9x10-12 cm3molecule-1s-1.
Infrared Insights into the Effect of Cholesterol on Lipid Membranes Chem. Phys. (IF 1.767) Pub Date : 2017-12-21 P. Stevenson, A. Tokmakoff
Effect of Oligomer Length on Vibrational Coupling and Energy Relaxation in Double-Stranded DNA Chem. Phys. (IF 1.767) Pub Date : 2017-12-19 Gordon Hithell, Paul M. Donaldson, Gregory M. Greetham, Michael Towrie, Anthony W. Parker, Glenn A. Burley, Neil T. Hunt
Effect of different substitution position on the switching behavior in single-molecule device with carbon nanotube electrodes Chem. Phys. (IF 1.767) Pub Date : 2017-12-18 Jingjuan Yang, Xiaoxiao Han, Peipei Yuan, Baoan Bian, Yixiang Wang
Stark shift of impurity doped quantum dots: Role of noise Chem. Phys. (IF 1.767) Pub Date : 2017-12-16 Sk.Md. Arif, Aindrila Bera, Anuja Ghosh, Manas Ghosh
A computational investigation on the photo-isomerization of 2,4,6-octatriene and its UV-visible spectrum Chem. Phys. (IF 1.767) Pub Date : 2017-12-16 Anjan Chattopadhyay, Praveen Saini, Raymond Hakim, Adrian Komainda, Horst Köppel
The dynamical processes following photoexcitation of all-trans 2,4,6-octatriene to the two lowest singlet excited states are investigated theoretically, from two different points of view. The S1-S0 photoisomerization is characterized with a focus on structural aspects (stationary points and reactive modes), while for the UV-visible spectrum, arising from excitation to the S2 state, nonadiabatic quantum dynamics calculations with four planar degrees of freedom are performed. The underlying electronic structure data are obtained from CASSCF and MS-CASPT2 ab initio computations, the quantum dynamical calculations rely on the Multiconfiguration Time-Dependent Hartree (MCTDH) method. The observed envelope of the UV-visible spectrum is well reproduced and the substantial broadness of the spectral features related to a nonradiative S2-S1 transition proceeding within few tens of femtoseconds. The vertical excitation energy from the Ag to the Bu state shows a red-shift (∼0.2 eV with the cc-pVTZ basis set) with reference to the all-trans hexatriene system. This affects the S2-S1 nonradiative decay, while the methylation of the terminal carbon atoms seems to have a minor influence on the photo-isomerization path.
Theoretical and Experimental Study of Electron-deficient Core Substitution Effect of Diketopyrrolopyrrole Derivatives on Optoelectrical and Charge Transport Properties Chem. Phys. (IF 1.767) Pub Date : 2017-12-16 Guodong Ding, Asif Mahmood, Ailing Tang, Fan Chen, Erjun Zhou
Analysis of paramagnetic 3d ions (Cr3+ and Fe3+) centers in fluoroelpasolite Cs2NaGaF6 crystal by both DFT and SPM calculations Chem. Phys. (IF 1.767) Pub Date : 2017-12-15 D. Erbahar, Y. Emül, M. Açıkgöz
Adsorption studies of trimethyl amine and n-butyl amine vapors on stanene nanotube molecular device – a first-principles study Chem. Phys. (IF 1.767) Pub Date : 2017-12-08 R. Bhuvaneswari, V. Nagarajan, R. Chandiramouli
The stanene nanotube is designed and used for the detection of trimethyl amine (TMA) and n-butyl amine (n-BA) vapors, which is investigated using first-principles study. The electronic properties of bare stanene nanotube and the adsorption properties of TMA and n-BA molecules are studied using density functional theory with non-equilibrium Green’s function. Moreover, the device density of states shows the shift in the peak maxima upon adsorption of TMA and n-BA molecules on to the stanene nanotube. The variation in the flow of electron is noticed upon adsorption of TMA and n-BA molecules in the transmission spectrum of stanene nanotube. I-V characteristics clearly confirm the variation in the current upon adsorption of TMA and n-BA molecules. The findings of the study clearly suggest that the stanene nanotube molecular device can be used for the detection of trace levels of TMA and n-BA molecules present in the atmosphere.
Monolayer Adsorption of Noble Gases on Graphene Chem. Phys. (IF 1.767) Pub Date : 2017-12-06 Sidi M. Maiga, Silvina M. Gatica
We report our results of simulations of the adsorption of noble gases (Kr, Ar, Xe) on graphene. For Kr, we consider two configurations: supported and free-standing graphene , where atoms are adsorbed only on one or two sides of the graphene. For Ar and Xe, we studied only the case of supported graphene. For the single-side adsorption, we calculated the two-dimensional gas-liquid critical temperature for each adsorbate. We determined the different phases of the monolayers and constructed the phase diagrams. We found two-dimensional incommensurate solid phases for krypton, argon and xenon, and a two-dimensional commensurate solid phase for krypton. For double side adsorption of Kr, we do not see evidence of an ordering transition driven by the interlayer forces.
Recognition of Anions using urea and thiourea substituted calixarenes: A DFT assessment of Non-Covalent Interactions Chem. Phys. (IF 1.767) Pub Date : 2017-12-06 Mohd. Athar, Mohsin Y. Lone, Prakash C. Jha
Designing of new calixarene receptors for the selective binding of anions is an age-old concept; even though expected outcomes from field are at premature stage. Therefore, quantum chemical calculations were performed for providing structural basis of anion binding with urea and thiourea substituted calixarenes (1,2, and 3). In particular, spherical halides (F-, Cl-, Br-) and linear anions (CN-, N3-, SCN-) were modelled for calculating binding energies with receptor 1, 2 and 3 followed by their marked IR vibrations; taking the available experimental information into account. We found that the thiourea substitutions have better capability to stabilize the anions. However, the structural behaviour of macrocyclic motifs were responsible for displaying the anion binding potentials. Further, second order “charge transfer” interactions of n‐σ∗NH and n‐σ∗OH type along the H‐bond axis played critical role in developing hydrogen bonds. In addition, thermodynamic properties, non-covalent interactions (NCI), chemical-reactivity descriptors and NCI index were discussed.
The Role of Near Resonance Electronic Energy Transfer on the Collisional Quenching of NO (A2Σ+) by C6H6 and C6F6 at Low Temperature Chem. Phys. (IF 1.767) Pub Date : 2017-12-05 Joshua D. Winner, Niclas A. West, Madison H. McIlvoy, Zachary D. Buen, Rodney D.W. Bowersox, Simon W. North
We present measurements of the collisional fluorescence quenching cross section of NO (A2Σ+) by benzene and hexafluorobenzene at a series of temperatures using a custom built slow flow cell and a pulsed de Laval nozzle test cell. The measurements show a deviation from the common harpoon mechanism of collisional fluorescence quenching, specifically the large quenching cross section of 147 Å2 at 300 K measured for benzene which is not predicted by the harpoon mechanism due to the low electron affinity of benzene (-1.5 eV). We speculate that the quenching of NO (A2Σ+) by benzene and hexafluorobenzene occurs through near resonance electronic energy transfer from the NO A-state to the A-state of the quencher via a pseudo-emission process. The predicted T-1/3 dependence of the cross section for this model is consistent with the experimental observations.
Insight Into The New Excited-State Intramolecular Proton Transfer (ESIPT) Mechanism of N,N’-bis(salicylidene)-p-phenylenediamine (p-BSP) Chem. Phys. (IF 1.767) Pub Date : 2017-12-02 Jiaojiao Hao, Yang Yang
A new excited-state intramolecular proton transfer (ESIPT) mechanism of N,N’-bis(salicylidene)-p-phenylenediamine (p-BSP) including the single and double ESIPT processes has been proposed using the time-dependent density functional theory (TDDFT) method, which was clearly different from the one proposed previously (Ziółek et al. J. Phys. Chem. A. 2009, 113, 2854). By analyzing the bond lengths, bond angles and IR vibrational spectra, we determined that two intramolecular hydrogen bonds (IHBs) (O1−H2···N3 and O4−H5···N6) of p-BSP were strengthened in the S1 state, which could facilitate the ESIPT process. Additionally, intramolecular charge transfer based on the frontier molecular orbitals (MOs) and the map of the electron density difference between the S0 and S1 states demonstrated the possibility ESIPT reaction. To reveal the detailed ESIPT mechanism, we constructed potential energy surfaces (PESs) in the S0 and S1 states, and thus determined that the single and double ESIPT processes coexisted in the S1 state.
Bosonic quantum dynamics following a linear interaction quench in finite optical lattices of unit filling Chem. Phys. (IF 1.767) Pub Date : 2017-12-02 S.I. Mistakidis, G.M. Koutentakis, P. Schmelcher
The nonequilibrium ultracold bosonic quantum dynamics in finite optical lattices of unit filling following a linear interaction quench from a superfluid to a Mott insulator state and vice versa is investigated. The resulting dynamical response consists of various inter and intraband tunneling modes. We find that the competition between the quench rate and the interparticle repulsion leads to a resonant dynamical response, at moderate ramp times, being related to avoided crossings in the many-body eigenspectrum with varying interaction strength. Crossing the regime of weak to strong interactions several transport pathways are excited. The higher-band excitation dynamics is shown to obey an exponential decay possessing two distinct time scales with varying ramp time. Studying the crossover from shallow to deep lattices we find that for a diabatic quench the excited band fraction decreases, while approaching the adiabatic limit it exhibits a non-linear behavior for increasing height of the potential barrier. The inverse ramping process from strong to weak interactions leads to a melting of the Mott insulator and possesses negligible higher-band excitations which follow an exponential decay for decreasing quench rate. Finally, independently of the direction that the phase boundary is crossed, we observe a significant enhancement of the excited to higher-band fraction for increasing system size.
A DFT study of the electronic structures and optical properties of (Cr, C) co-doped rutile TiO2 Chem. Phys. (IF 1.767) Pub Date : 2017-11-29 Hao Chen, Xuechao Li, Rundong Wan, Sharon Kao-Walter, Ying Lei
To get an effective doping model of rutile TiO2, we systematically study geometrical parameters, density of states, electron densities, dielectric functions, optical absorption spectra for the pure, C mono-doping, Cr mono-doping and (Cr,C) co-doping rutile TiO2, using density functional calculations. We find that a C doped system presents higher stability under Ti-rich condition, while Cr doped and (Cr,C) co-doped systems are more stable under O-rich condition. For (Cr,C) co-doping situation, the imaginary part of the dielectric function reflects the higher energy absorption efficiency for incident photons. Moreover, co-doping system exhibits much bigger red-shift of optical absorption edge compared with Cr/C single doping systems, because of the great reduction of the direct band gap. The calculated optical absorption spectra show that the (Cr,C) co-doping rutile TiO2 has higher photocatalytic activity in the visible light region.
Dynamical behavior of molecular partial charges implied by the far-infrared spectral profile of liquid water Chem. Phys. (IF 1.767) Pub Date : 2017-11-24 Hajime Torii
On the basis of the successful reproducibility of the band at ∼200 cm-1 (6 THz) in the far-infrared (terahertz) spectrum of liquid water by spectral simulations, and the intermolecular charge flux as the primary mechanism giving rise to the intensity of this band, the dynamical behavior of the molecular partial charges in liquid water implied by the presence of this band is examined theoretically. The molecular partial charges are typically within the range of ±0.03 e, with frequent short-time (< 0.1 ps) excursions out of this range, and are rapidly modulated with a time constant of ∼0.12 ps. The long-time behavior of the time correlation function in the 0.3–10 ps region is related to the topological nature of the related molecular motions. The implication of the results on the use of time-domain terahertz spectroscopy to detect the properties of molecular motions in various environments is discussed.
Complementary experimental-simulational study of surfactant micellar phase in the extraction process of metallic ions: effects of temperature and salt concentration Chem. Phys. (IF 1.767) Pub Date : 2017-11-24 Alan Gustavo Soto-Ángeles, María del Rosario Rodríguez-Hidalgo, César Soto-Figueroa, Luis Vicente
The thermoresponsive micellar phase behaviour that exhibits the Triton-X-100 micelles by temperature effect and addition of salt in the extraction process of metallic ions was explored from mesoscopic and experimental points. In the theoretical study, we analyse the formation of Triton-X-100 micelles, load and stabilization of dithizone molecules and metallic ions extraction inside the micellar core at room temperature; finally, a thermal analysis is presented. In the experimental study, the spectrophotometric outcomes confirm the solubility of the copper-dithizone complex in the micellar core, as well as the extraction of metallic ions of aqueous environment via a cloud-point at 332.2 K. The micellar solutions with salt present a low absorbance value compared with the micellar solutions without salt. The decrease in the absorbance value is attributed to a change in the size of hydrophobic region of colloidal micelles. All transitory stages of extraction process are discussed and analysed in this document.
Influence of acceptor on charge mobility in stacked π- conjugated polymers Chem. Phys. (IF 1.767) Pub Date : 2017-11-24 Shih-Jye Sun, Miroslav Menšík, Petr Toman, Alessio Gagliardi, Karel Král
We present a quantum molecular model to calculate mobility of π-stacked P3HT polymer layers with electron acceptor dopants coupled next to side groups in random position with respect to the linear chain. The hole density, the acceptor LUMO energy and the hybridization transfer integral between the acceptor and polymer were found to be very critical factors to the final hole mobility. For a dopant LUMO energy close and high above the top of the polymer valence band we have found a significant mobility increase with the hole concentration and with the dopant LUMO energy approaching the top of the polymer valence band. Higher mobility was achieved for small values of hybridization transfer integral between polymer and the acceptor, corresponding to the case of weakly bound acceptor. Strong couplings between the polymer and the acceptor with Coulomb repulsion interactions induced from the electron localizations was found to suppress the hole mobility.
Computational study of red- and blue- shifted C●H···Se hydrogen bond in Q3C-H···SeH2 (Q = Cl, F, H) complexes Chem. Phys. (IF 1.767) Pub Date : 2017-11-22 Pragya Chopra, Shamik Chakraborty
This work presents C-H···Se hydrogen bonding interaction at the MP2 level of theory. The system Q3C-H···SeH2 (Q = Cl, F, and H) provides an opportunity to investigate red- and blue- shifted hydrogen bonds. The origin of the red- and blue- shift in C-H stretching frequency has been investigated using Natural Bond Orbital analysis. A large amount of electron density is being transferred to the σ∗C-H orbital in red-shifted Cl3C-H···SeH2. Electron density transfer in the blue-shifted F3C-H···SeH2 is primarily to the remote fluorine atoms. Further, due to polarization of the C-H bond, the contradicting effects of rehybridization and hyperconjugation are important. The extent of hyperconjugation reigns predominant in explaining the nature of the C-H···Se hydrogen bond in Q3C-H···SeH2 complexes as the hydrogen bond acceptor remain same in this investigation. Red- and blue- shift in Q3C-H···SeH2 (Q = Cl and F) complexes is best described by pro-improper hydrogen bond donor concept.
On the Solvation of Hydronium by Carbon Dioxide: Structural and Infrared Spectroscopic Study of (H3O+)(CO2)n Chem. Phys. (IF 1.767) Pub Date : 2017-11-22 Jianpeng Yang, Xiangtao Kong, Ling Jiang
Hydronium (H3O+) is the smallest member of protonated water. In this work, we use quantum chemical calculations to explore the solvation of H3O+ by adding one CO2 molecule at a time. The effect of stepwise solvation on infrared spectroscopy, structure, and energetics has been systematically studied. It has been found that the first solvation shell of H3O+ is completed at n = 6. Besides the hydrogen-bond interaction, the --- intermolecular interaction is also responsible for the stabilization of the larger clusters. The transfer of the proton from H3O+ onto CO2 with the formation of the OCOH+ moiety is not observed in the early stage of solvation process. Calculated IR spectra suggest that vibrational frequencies of H-bonded O-H stretching would afford a sensitive probe for exploring the early stage solvation of hydronium by carbon dioxide. IR spectra for the (H3O+)(CO2)n (n = 17) clusters could be measured by the infrared photodissociation spectroscopic technique and thus provide a vivid physical picture about how carbon dioxide solvates the hydronium.
Isosteric heat of water adsorption and desorption in homoionic alkaline-earth montmorillonites Chem. Phys. (IF 1.767) Pub Date : 2017-11-21 M. Belhocine, A. Haouzi, G. Bassou, T. Phou, D. Maurin, J.L. Bantignies, F. Henn
The aim of the present work is to study by means of thermodynamic measurements and Infrared spectroscopy, the effect of the interlayer cations on the adsorption-desorption of water in the case of a montmorillonite exchanged with alkaline-earth metals. For the first time, the net isosteric heat of water adsorption and desorption is determined from isotherms recorded at three temperatures. The net isosteric heat is a very useful parameter for getting more insights into the sorption mechanism since it provides information about the sorption energy evolution which can be complementary to that obtained from structural or gravimetric measurements. The homoionic montmorillonite samples are prepared from purification and cationic exchanged in aqueous solution of the raw material, i.e the reference SWy-2 Wyoming material. XRD at the dry state and elemental chemical analysis confirm that the treatment does not deteriorate the clay structure and yield the expected homoionic composition. The sorption isotherms measured at various temperatures show that the nature of the interlayer, i.e. exchangeable, cation changes the adsorbed/desorbed amount of water molecules for a given water relative pressure. The total amount of water adsorbed at P P ∘ = 0.5 follows the cation sequence Ca>Mg>Ba. Although the adsorption isosteric heat also follows the cation sequence Ca>Mg>Ba, that of desorption obeys a slightly different sequence Ca∼Mg>Ba. This discrepancy between the adsorption and desorption heat is due to the higher irreversibility of water sorption process in the Ca exchanged montmorillonite. Finally, analysis of the IR spectra recorded at room temperature and under a primary vacuum reveals that the amount of adsorbed water follows the same sequence as that of the isosteric heat of adsorption and shows the coexistence of liquid-like and solid-like water confined in the interlayer space.
Accuracy of Potfit-based potential representations and its impact on the performance of (ML-)MCTDH Chem. Phys. (IF 1.767) Pub Date : 2017-11-21 Frank Otto, Ying-Chih Chiang, Daniel Pelàez
Quantum molecular dynamics simulations with MCTDH or ML-MCTDH perform best if the potential energy surface (PES) has a sum-of-products (SOP) or multi-layer operator (MLOp) structure. Here we investigate four different POTFIT-based methods for representing a general PES as such a structure, among them the novel random-sampling multi-layer Potfit (RS-MLPF). We study how the format and accuracy of the PES representation influences the runtime of a benchmark (ML-)MCTDH calculation, namely the computation of the ground state of the H 3 O 2 - ion. Our results show that compared to the SOP format, the MLOp format leads to a much more favorable scaling of the (ML-)MCTDH runtime with the PES accuracy. At reasonably high PES accuracy, ML-MCTDH calculations thus become up to 20 times faster, and taken to the extreme, the RS-MLPF method yields extremely accurate PES representations (global root-mean-square error of ∼ 0.1 cm - 1 ) which still lead to only moderate computational demands for ML-MCTDH.
S⋯N chalcogen bonded complexes of carbon disulfide with diazines. Theoretical study Chem. Phys. (IF 1.767) Pub Date : 2017-11-21 Wiktor Zierkiewicz, Jindřich Fanfrlík, Mariusz Michalczyk, Danuta Michalska, Pavel Hobza
Carbon disulfide complexes with diazine (pyridazine, pyrimidine or pyrazine) have been studied by density functional BLYP-D3 and ab initio CCSD(T) methods. All possible conformers of these complexes have been found. In the chalcogen bonded complexes, the CCSD(T)/cc-pvtz calculated interaction energies (ΔE) range between -0.89 and -2.19 kcal mol-1. These complexes are more stable than those stabilized by hydrogen bond. The linear correlation between the ΔE and the most negative values of the electrostatic potential surfaces (Vs,min) on the nitrogen atom of the diazines has been found. According to the symmetry-adapted perturbation theory (SAPT) analysis, in the chalcogen bonded complexes among all of the attraction forces the electrostatic component is the most important one, while in the hydrogen bonded and stacking complexes the dispersion contribution is the leading term. Moreover, the Natural Bond Orbitals (NBO), AIM and Noncovalent Interaction Index (NCI) analyses have been performed.
Diffusion of Brownian particles in a tilted periodic potential under the influence of an external Ornstein-Uhlenbeck noise Chem. Phys. (IF 1.767) Pub Date : 2017-11-21 Zhan-Wu Bai, Wei Zhang
The diffusion behaviors of Brownian particles in a tilted periodic potential under the influence of an internal white noise and an external Ornstein-Uhlenbeck noise are investigated through numerical simulation. In contrast to the case when the bias force is smaller or absent, the diffusion coefficient exhibits a nonmonotonic dependence on the correlation time of the external noise when bias force is large. A mechanism different from locked-to-running transition theory is presented for the diffusion enhancement by a bias force in intermediate to large damping. In the underdamped regime and the absence of external noise, the diffusion coefficient is a monotonically decreasing function of low temperature rather than a nonmonotonic function when external noise is absent. The diffusive process undergoes four regimes when bias force approaches but is less than its critical value and noises intensities are small. These behaviors can be attributed to the locked-to-running transition of particles.
Concerted-asynchronous reaction path of the excited-state double proton transfer in the 7-azaindole homodimer and 6H-indolo[2,3-b]quinoline/7-azaindole heterodimer Chem. Phys. (IF 1.767) Pub Date : 2017-11-13 Shohei Yamazaki
Reaction path of the excited-state double proton transfer (ESDPT) in the homodimer of 7-azaindole (7AI2 homodimer) and heterodimer of 6H-indolo[2,3-b]quinoline and 7-azaindole (6HIQ-7AI heterodimer) is computationally studied by means of intrinsic reaction coordinate (IRC) calculations. The IRC path determined at the TDDFT level predicts the concerted-asynchronous mechanism for the ESDPT in 6HIQ-7AI as well as in 7AI2, where the N-H⋯ ⋯ N hydrogen bonds exhibit asymmetric structures along the reaction path with a single energy barrier. The IRC calculations at the CIS level, however, exhibits a local minimum for single-proton-transferred intermediate, suggesting the stepwise mechanism. Single-point energy calculations at the RI-CC2 level reproduce the TDDFT results, but do not the CIS results. On the basis of potential-energy profiles calculated against intermolecular distance, the discrepancy between the TDDFT and CIS methods is likely attributed to the underestimation of intermolecular interaction energy in the latter method due to the lack of dynamical electron correlation.
6.2 μm Spectrum and 6-Dimensional Morphed Potentials of OC-H2O Chem. Phys. (IF 1.767) Pub Date : 2017-11-13 Luis A. Rivera-Rivera, Blake A. McElmurry, Kevin W. Scott, Sean D. Springer, Robert R. Lucchese, John W. Bevan, Igor I. Leonov, Laurent H. Coudert
Rovibrational transitions associated with tunneling states in the ν5 (water bending) vibration of the OC-H2O complex have been recorded using a supersonic jet mode-hop free quantum cascade laser spectrometer at 6.2 μm. Analysis of the resulting spectra is facilitated by incorporating fits of previously recorded microwave and submillimeter data accounting for Coriolis coupling. The theoretical basis of morphing a 5-D frozen monomers potential was initially developed and then extended to two 6-D morphed potentials. A combination of these spectroscopic results and previous rovibrational data for the ν5 vibration in OC-D2O are then used to generate a 6-D morphed potential surface for the intermolecular and the water bending vibrations. An alternative 6-D morphed potential of the intermolecular and the ν3 (CO stretching) vibrations was also generated. These determined morphed potentials then formed the basis for modeling the dynamics of the complex and prediction of accurate intermolecular rovibrational frequencies of the complex.
Predicting Glass-to-Glass and Liquid-to-Liquid Phase Transitions in Supercooled Water using Classical Nucleation Theory Chem. Phys. (IF 1.767) Pub Date : 2017-11-13 Robert F. Tournier
Glass-to-glass and liquid-to-liquid phase transitions are observed in bulk and confined water, with or without applied pressure. They result from the competition of two liquid phases separated by an enthalpy difference depending on temperature. The classical nucleation equation of these phases is completed by this quantity existing at all temperatures, a pressure contribution, and an enthalpy excess. This equation leads to two homogeneous nucleation temperatures in each liquid phase; the first one (Tn- below Tm) being the formation temperature of an “ordered” liquid phase and the second one corresponding to the overheating temperature (Tn+ above Tm). Thermodynamic properties, double glass transition temperatures, sharp enthalpy and volume changes are predicted in agreement with experimental results. The first-order transition line at TLL=0.833×Tm between fragile and strong liquids joins two critical points. Glass phase above Tg becomes “ordered” liquid phase disappearing at TLL at low pressure and at Tn+=1.302×Tm at high pressure.
Tolman’s length and limiting supersaturation of vapor Chem. Phys. (IF 1.767) Pub Date : 2017-11-13 Nikolay V. Alekseechkin
The classical Kelvin formula for the equilibrium vapor pressure over a droplet of radius R R is extended to small radii and vapor non-ideality, from where the limiting supersaturation condition is obtained by relating the point R=0 R = 0 to the value of limiting (spinodal) supersaturation of vapor. The analysis of different dependences of the Tolman length on radius, δ(R) δ ( R ) , obeying this condition suggests that (i) the value of δ(0) δ ( 0 ) is positive and the function δ(R) δ ( R ) decreases with increasing radius; (ii) the curvature effect (the dependence of surface tension on radius) in the nucleation region is determined by the value of δ(0) δ ( 0 ) . At the same time, this effect is weakly sensitive to the form of the function δ(R) δ ( R ) and insensitive to its asymptotic value δ∞ δ ∞ .
Binding affinity of the L-742,001 inhibitor to the endonuclease domain of A/H1N1/PA influenza virus variants: Molecular simulation approaches Chem. Phys. (IF 1.767) Pub Date : 2017-11-11 Hung Nguyen, Hoang Linh Nguyen, Huynh Quang Linh, Minh Tho Nguyen
The steered molecular dynamics (SMD), molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) and free energy perturbation (FEP) methods were used to determine the binding affinity of the L-742,001 inhibitor to the endonuclease domain of the A/H1N1/PA influenza viruses (including wild type (WT) and three mutations I79L, E119D and F105S for both pH1N1 PA and PR8 PA viruses). Calculated results showed that the L-742,001 inhibitor not only binds to the PR8 PAs (1934 A influenza virus) better than to the pH1N1 PAs (2009 A influenza virus) but also more strongly interacts with the WT endonuclease domain than with three mutant variants for both pH1N1 PA and PR8 PA viruses. The binding affinities obtained by the SMD, MM-PBSA and FEP methods attain high correlation with available experimental data. Here the FEP method appears to provide a more accurate determination of the binding affinity than the SMD and MM-PBSA counterparts.
Excited State Properties of 2'-Hydroxychalcone Analogues Functionalized with a Diene Moiety Studied by Steady State and Laser Flash Photolysis Chem. Phys. (IF 1.767) Pub Date : 2017-11-11 Yukino Shinozaki, Minoru Yamaji, Tatsuo Arai
2'-Hydroxychalcone (HC) analogues 1 and 2 having a diene part tethering the phenyl and naphthyl chromophores, respectively, were prepared, and their photochemical and photophysical properties were studied. Fluorescence from these compounds was absent in solution and the solid state. Based on the results obtained upon steady state and laser flash photolyses, compound 2 was found to be substantially stable on photoirradiation without undergoing intersystem crossing to the triplet state whereas compounds 1 showed transient absorption due to the triplet tautomer. The deactivation processes in the excited states were discussed by considering energetic reaction diagrams for the corresponding tautomers and isomers.
MCTDH Study on the Reactive Scattering of the Cl + HD Reaction based on the Neural-Networks Potential Energy Surface ☆ Chem. Phys. (IF 1.767) Pub Date : 2017-11-11 Qingyong Meng
To study the dynamics resonances of the Cl + HD reaction which was proposed to proceed via abstraction mechanism with no clear resonances, we perform dynamics calculations by the multiconfiguration time-dependent Hartree (MCTDH) method based on recently developed neural-networks potential energy surface (Science347 (2015), 60). The HD molecule in v=0 v = 0 (GS), v=1 v = 1 (EX1), v=2 v = 2 (EX2), and v=3 v = 3 (EX3) states is used for the reactant. For GS, no distinctive resonance peak is found, while for EX1 two distinctive peaks at kinetics energies of 0.11 0.11 and 0.17 0.17 eV are investigated. These resonance peaks are well consistent with the previous results (Science347 (2015), 60). Moreover, the present MCTDH calculations predict well-marked resonance peaks at 0.04,0.05,0.07 0.04 , 0.05 , 0.07 , and 0.10 0.10 eV for EX2 and EX3, which indicates that anticipation of the chemical bond softening model (Science327 (2010), 1501) is confirmed in this work.
Molecular dynamics simulation of the thermosensitivity of the human connexin 26 hemichannel Chem. Phys. (IF 1.767) Pub Date : 2017-11-09 Hadi Alizadeh, Jamal Davoodi, Carsten Zeilinger, Hashem Rafii-Tabar
Connexin hemichannels mediate cytoplasm and extracellular milieu communication by exchanging a variety of cytoplasmic molecules and ions. These hemichannels can be regulated by external stimuli such as mechanical stress, applied voltage, pH and temperature changes. Although there are many studies on structures and functions of connexin 26 in contexts of pH, ion concentration and voltage, employing computational methods, no such study has been performed so far involving temperature changes. In this study, using molecular dynamics simulation, we investigate thermosensitivity of the human Connexin 26 hemichannel. Our results show that the channel approaches a structurally closed state at lower temperature compared to higher temperature. This is in fair agreement with experimental results that indicate channel closure at lower temperature. Furthermoer, our MD simulation results show that some regions of connexin 26 hemichannel are more sensitive to temperature compared to other regions. Whereas the intercellular half of the channel does not show any considerable response to temperature during the simulation time accessible in this study, the cytoplasmic half approaches a closed structural state at lower temperature compared to the higher temperature. Specifically, our results suggest that the cytoplasmic loop, the cytoplasmic half of the second transmembrane helix, and the N-terminus helix play a dominant role in temperature gating.
Radiative decay of HeLi+(b3∑+ ∑ + ) Chem. Phys. (IF 1.767) Pub Date : 2017-11-08 Martina Zámečníková, Pavel Soldán
Radiative lifetimes of the ro-vibrational bound states of HeLi+ HeLi + (b3∑+ b 3 ∑ + ) are calculated quantum-mechanically when both bound-bound and bound-free processes are taken into account. The calculations are restricted to the initial states with low rotational quantum numbers. For the rotationless molecular ion, the shortest lifetime is 1.30×10-6s 1.30 × 10 - 6 s of the ground vibrational state. With increasing vibration excitations the radiative lifetimes slightly increase, but keep below 10-5s 10 - 5 s for next 17 vibrational states, then they start to increase more rapidly up to 2.41×10-2s 2.41 × 10 - 2 s for the highest vibrational state. The radiative lifetimes also tend to slightly prolong with increasing rotation excitations but stay on the same magnitude for the low rotational quantum numbers.
A multimode-like scheme for selecting the centers of Gaussian basis functions when computing vibrational spectra Chem. Phys. (IF 1.767) Pub Date : 2017-10-23 Sergei Manzhos, Xiaogang Wang, Tucker Carrington Jr
Predictive methods of some optoelectronic properties for blends based on quaternized polysulfones Chem. Phys. (IF 1.767) Pub Date : 2017-10-23 Adina Maria Dobos, Anca Filimon
Quasirelativistic potential energy curves and transition dipole moments of NaRb Chem. Phys. (IF 1.767) Pub Date : 2017-10-21 M. Wiatr, P. Jasik, T. Kilich, J.E. Sienkiewicz, H. Stoll
We report on extensive calculations of quasi-relativistic potential energy curves and, for the first time, transition dipole moments including spin-orbit and scalar-relativistic effects of the NaRb molecule. The calculated curves of the 0+ 0 + , 0- 0 - , 1, 2 and 3 molecular states correlate for large internuclear separation with the fourteen lowest atomic energies up to the Na(3s2 s 2 S1/2 S 1 / 2 )+Rb(7s2 s 2 S1/2 S 1 / 2 ) atomic limit. Several new features of the potential energy curves have been found.
Dynamic interference in the resonance-enhanced multiphoton ionization of hydrogen atoms by short and intense laser pulses Chem. Phys. (IF 1.767) Pub Date : 2017-10-21 Anne D. Müller, Eric Kutscher, Anton N. Artemyev, Lorenz S. Cederbaum, Philipp V. Demekhin
Photoionization of the hydrogen atom by intense and short coherent laser pulses is investigated from first principles by a numerical solution of the time-dependent Schrödinger equation in the dipole-velocity gauge. The considered photon energies are resonant to the 1s→2p 1 s → 2 p excitation, and the pulse intensities are high enough to induce Rabi floppings. The computed resonance-enhanced two-photon ionization spectra as well as the three-photon above threshold ionization spectra exhibit pronounced multiple-peak patterns due to dynamic interference. Fingerprints of dynamic interference can also be seen directly in the radial density of the photoelectron. The impact of the variation of the pulse intensity and photon energy on the dynamic interference is investigated, and the angular distribution of the emitted electrons is analyzed in some details. The present precise numerical results confirm our previous theoretical predictions on the two-photon ionization spectra [Phys. Rev. A 86 (2012) 063412] made within a minimal few-level model.
A quantum dynamical study of the photoelectron spectra and the Renner-Teller effect in BrCN and ClCN based on four-component potential energy hypersurfaces Chem. Phys. (IF 1.767) Pub Date : 2017-10-12 V.A. Tran, M. Pernpointner
In this work we investigate the Renner-Teller effect (RTE) in the photoelectron spectra of ClCN and BrCN. The spectra were calculated by a nuclear wave packet propagation on coupled cationic Π1/2/Π3/2 Π 1 / 2 / Π 3 / 2 surfaces obtained by the four-component Fock-space coupled cluster method. The scalar relativistic, spin-orbit and electron correlation effects are consistently included in the hypersurfaces for the three internal nuclear degrees of freedom. In contrast to other approaches no coupling matrix elements involving the spin-orbit operator together with an explicit representation of the wave function were necessary. The current study extends earlier work on the RTE for the derivation of the Renner-Teller parameters c and d where only one nuclear degree of freedom was considered [J. Phys. B 46, 125101 (2013)]. The outlined procedure is especially useful for electronic structure methods that yield accurate energies but do not provide an explicit wave function representation.
183W nuclear dipole moment determined by gas-phase NMR spectroscopy Chem. Phys. (IF 1.767) Pub Date : 2017-10-10 Piotr Garbacz, Włodzimierz Makulski
Controlling harmonic distributions from H2+ driven by linearly and circularly polarized laser fields Chem. Phys. (IF 1.767) Pub Date : 2017-10-07 Liqiang Feng, Yi Li, Hang Liu
The spatial distributions of the high-order harmonics from H2+ driven by the linearly and the circularly polarized laser fields have been theoretically investigated. It is found that when the molecular axis parallels to the polarized direction of the linearly polarized laser field, the contributions of the harmonics are mainly from the negative-H and the positive-H for the cases of E(t) > 0 and E(t) < 0, respectively. As the angle between the molecular axis and the linearly polarized laser field increases, the contributions of the harmonics from the negative-H are enhanced and play the main role in the harmonic spectrum. Further, with the introduction of the controlling circularly polarized laser field, the intensity enhancement of the harmonics from the positive-H can be achieved. Moreover, the contributions of the harmonics from the two-H nuclei are sensitive to the ellipticity of the laser field. Finally, the time-frequency analyses of the harmonics and the time-dependent electron locations have been given to explain the physical mechanism behind the spatial distributions of the harmonics from the two-H nuclei of H2+.
Probing adsorption sites of carbon dioxide in metal organic framework of [Zn(bdc)(dpds)]n: A molecular simulation study Chem. Phys. (IF 1.767) Pub Date : 2017-09-25 Shih-I Lu, Jian-Min Liao, Xiao-Zhuang Huang, Chia-Hsun Lin, Szu-Yu Ke, Chih-Chieh Wang
We used force-field based grand-canonical Monte Carlo simulation method and density functional theory to study adsorption characteristics of carbon dioxide (CO2) molecules in a metal-organic framework (MOF) compound, [Zn(bdc)(dpds)]n. The studied MOF include a metal ion (Zn(II)), an anion organic linker (dianion of benzene dicarboxylicacid, bdc2−) and a neutral organic linker (4,4’-dipyridyldisulfide, dpds). Results from calculated adsorption isotherms and enthalpies of adsorption agree with the experimental data. The interactions between the adsorbed CO2 and the organic linkers were examined in simulations. Calculated results show available absorption sites are surrounded by two dpds ligands in which an S-S bond as an N-N' spacer connect two pyridines. In contrast, the bdc2− ligand does not give a significant contribution to the substantial adsorption amount even though it contains the carboxylate group that provides available bonding site to CO2.
The Effect of Site-Specific Spectral Densities on the High-Dimensional Exciton-Vibrational Dynamics in the FMO Complex Chem. Phys. (IF 1.767) Pub Date : 2017-09-23 Jan Schulze, Mohamed F. Shibl, Mohammed J. Al-Marri, Oliver Kühn
The coupled exciton-vibrational dynamics of a three-site model of the FMO complex is investigated using the Multi-layer Multi-configuration Time-dependent Hartree (ML-MCTDH) approach. Emphasis is put on the effect of the spectral density on the exciton state populations as well as on the vibrational and vibronic non-equilibrium excitations. Models which use either a single or site-specific spectral densities are contrasted to a spectral density adapted from experiment. For the transfer efficiency, the total integrated Huang-Rhys factor is found to be more important than details of the spectral distributions. However, the latter are relevant for the obtained non-equilibrium vibrational and vibronic distributions and thus influence the actual pattern of population relaxation.
Effects of adding LiBF4 on the glass-transition kinetics of 1,2-propanediol Chem. Phys. (IF 1.767) Pub Date : 2017-09-20 Yukio Terashima, Kiyoshi Takeda
First-Principles Investigation of Decomposition and Adsorption Properties of RDX on the Surface of MgH2 Chem. Phys. (IF 1.767) Pub Date : 2017-09-18 RAO Guo-Ning, YAO Miao, PENG Jin-Hua
Surface adsorption and decomposition mechanisms of cyclotrimethylenetrinitramine (RDX) molecules on the MgH2 (110) crystal face are investigated in this paper by employing the First-Principles. With the N-NO2 bond of RDX molecules as a reference, 12 adsorption sites are considered that are vertical (V1-V6) and parallel (P1-P6) to the MgH2 (110) surface. Results show that these 12 types of adsorption of RDX molecules on the MgH2 (110) crystal face are all chemical adsorption with high heat release, where the vertical Mg-top position (V1) is the most stable adsorption configuration. In all the 12 types of chemical adsorption, RDX molecules are decomposed, through 4 mechanisms including bis-nitro mono-N-O bond rupture, mono-nitro mono-N-O bond rupture, mono-nitro bis-N-O bond rupture and mono-N-O2 bond rupture, where the V-type adsorption is due to N-O bond rupture and the P-type adsorption is due to N-NO2 bond rupture, resulting in RDX decomposition. Secondly, in proximity to the Fermi level, the density of states of the RDX molecule highly coincides with that of the MgH2 (110) crystal face, which is prone to cause orbital hybridization and RDX decomposition. Also, the density of states in proximity to the Fermi level is mainly contributed by nitro O atoms and ring N atoms of RDX, as well as Mg atoms of the MgH2 (110) crystal face, and these 3 types of atoms are also active centers for chemical adsorption and decomposition reaction. Finally, an obvious phenomenon of charge transfer is present between Mg atoms in the first layer of the MgH2 (110) crystal face and O atoms in the nitro group of RDX. Also, the charge change in O and Mg atoms in the V configuration is greater than that in the P configuration, indicating that the V configuration has stronger interaction between RDX and the MgH2 (110) crystal face, and thus RDX in the V configuration is more prone to decomposition and the V configuration represents a better adsorption mode.
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