Elsevier

Chemical Physics

Volume 538, 1 October 2020, 110825
Chemical Physics

Theoretical study of the alkali hydride anions XH(X = Li, Na, and K)

https://doi.org/10.1016/j.chemphys.2020.110825Get rights and content

Highlights

  • For the alkali hydride molecular anions XH (X = Li, Na, K and Rb), we investigated:

  • Potential curves with the spectroscopic constants Te, Re, ωe, Be, αe, De.

  • Dipole moments, Franck-Condon factor.

  • Rovibrational parameters Ev, Bv, Dv, Rmin, Rmax.

Abstract

The electronic structure of the alkali hydride anions (LiH-, NaH-, and KH-), has been investigated via ab initio CASSCF/(MRCI + Q) and R-Matrix method calculations. Comparison between the results of the two calculation methods show that the pure bound state method may be unsuitable for the calculation of the electronic states of LiH- molecule, as the potential energy curves that it presents may be spurious. The adiabatic potential energy curves and the dipole moment curves of the low-lying electronic states of alkali hydride anionic molecules are investigated in the representation 2s+1Ʌ(+/-) where the percentage ionic character fionic around the equilibrium position of the ground state X2Σ+ has been calculated. Additionally, the spectroscopic constants Te, Re, ωe, Be, the dipole moment µe, and the dissociation energy De were computed for the bound states of the two molecules NaH- and KH-. The transition dipole moment curves for the lowest 2Σ+– 2Π transition have been also presented along with their Franck-Condon factor (FCF). A rovibrational study has been performed using the canonical functions approach in order to study the nuclear motion and find the rovibrational constants for the ground and several excited states. The diagonal Franck-Condon factor f00 may provide efficient routes for the formation of cold and ultracold molecules.

Graphical abstract

For the alkali hydride molecular anions XH (X=Li, Na, K and Rb), the potential energy curves in the representation 2s+1Λ(+/-) have been calculated along with the spectroscopic constants, the static and transition dipole moment, the Franck-Condon factor and the rovibrational calculations of the investigated electronic states.

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Section snippets

Introduction:

In the late 20th and early 21st centuries, there has been a remarkable development in physics fulfilled by the progress in the methods of producing and trapping of ultracold atoms in gaseous phase [1]. Thus, several techniques were implemented in order to manipulate and study ultracold matter via the optical and electromagnetic fields leading to developed frameworks for quantum information processes [2]. Regarding the cooling of molecular species, a new range of techniques has been developed

Pure bound state computational Approach:

By the employment of the state averaged Complete Active Space Self Consistent Field (CASSCF) followed by Multireference single and double configuration interaction (MRCI) method with Davidson correction (+Q) [36] the electronic states of the alkali hydride molecular anions LiH, NaH, and KH have been investigated in their doublet and quartet multiplicities. The calculation has been done by using the high-level ab initio calculations applied in MOLPRO program package [37] taking the advantage

R-Matrix method computational approach:

R-matrix method is employed in the calculation. The space is separated into an inner region which contains the molecule and its orbitals, and an outer region. In the inner region, the scattered electron is indistinguishable from the molecular electrons, and can occupy molecular orbitals [44].For molecules containing alkali metals, virtual orbitals are very diffuse. Care has to be taken to avoid linear dependencies between the continuum wave function and the virtual orbitals. A large R-matrix

Dipole bound States, stability and metastability

The adiabatic potential energy curves (PECs) that have been investigated using the pure bound state approach for the low lying electronic states of doublet and quartet multiplicities for the alkali hydride molecular anions XH (X = Li, Na, and K) and plotted as function of the internuclear separation respectively in Fig. 1, Fig. 2, Fig. 3 and Figs. (FS1-FS3) in the supplementary material. The origin is taken at -8.03 Hartree, -162.46 Hartree, and -599.75 Hartree for LiH, NaH, and KH

Conclusion:

For the alkali hydride molecular ions LiH, NaH, and KH, the potential energy curves have been investigated via spin free study by implementing MCSCF/MRCI and R-matrix technique. Comparison between R-matrix and pure bound state results have shown that the results related to the MCSCF/MRCI excited states of LiH- may be representative of NMFE states. Most of the doublet states of NaH -and KH- ions have deep potential wells while those of quartet states are entirely shallow. The spectroscopic

CRediT authorship contribution statement

Israa Zeid: Software, writting. Nayla El-Kork: Funding acquisition, Writing - review & editing. Sally Al Shawa: Data curation, Formal analysis. Mahmoud Korek: Supervision.

Acknowledgements

This publication is based upon work supported by the Khalifa University of Science and Technology under Award No. CIRA-2019-054. The authors would like to acknowledge the use of MASDAR High power computer, Khalifa University Nuclear Engineering Department High power computer and Ankabut High Power computer for the completion of their work. Also, the authors would like to acknowledge Quantemol team for pursuing the R-Matrix method calculations.

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