Research paperTheoretical partial ionization cross sections by electron impact for production of cations from CH3OH, CO2 and NH3
Graphical abstract
Total ionization cross sections (TICS) in 10−16 cm2 for CH3OH. Solid line, long dashed line, dotted line, dashed-dotted line and short dashed line represent the theoretical calculations of present, Vinodkumar et al. [33], Hudson (DM calculations) et al. [11], Deutsch et al. [20], Kumar et al. [30] and Pal [13]. Solid triangles, open circles, filled diamonds (blue), open stars (green) and filled squares (red) represent the experiment data of Nixon et al. [7], Rejoub et al. [12], Djuric et al. [14], Hudson (Exp.) et al. [19] and Srivastava et al. [11].
Introduction
The ionization cross sections of molecules have an importance in many applications such as astrophysics, atmospheric science biological science and plasma modelling [1], [2], [3]. Methanol is the smallest alcohol and has an importance as it can be supposed to be a prototype for larger alcohols. Interaction of methanol with electrons is a subject of interest because it can be used as fuel which is the alternative to traditional fossil fuels. This fuel releases less toxic and greenhouse gases on burning in the internal combustion engines in comparison of fossil fuels. The plasma modelling is required to make the theoretical model of car engines because the plasma is created during combustion of bio-fuel in the engines. The ionization cross sections may be used as input parameter [4], [5], [6], [7]. In industries, ammonia is used as the source of nitrogen to fabricate nitride films. Ammonia is also used to produce the N2-H2 plasma. Carbon dioxide is widely used in low temperature plasma devices in laboratories. Furthermore, these molecules are detected in the interstellar space medium and also in the atmosphere of planets in the solar system which play important role in the chemistry of these environments [8], [9], [10].
Total and partial electron impact ionization cross sections for CH3OH, CO2 and NH3 have been measured by a number of groups using the different experimental methods. Recently, Nixon et al. [7] have measured the electron impact absolute partial ionization cross sections of methanol by using quadrupole mass spectrometer. Srivastava et al. [11] have also investigated the experimental partial ionization cross sections for 10 cations of methanol by electron impact. Rejoub et al. [12] have measured the absolute partial ionization cross section for groups of cations CHnO+ (CH3OH+ + CH2OH+ + CH2O+ + CHO+ + CO+) and CHn+ + HnO+ (CH3+ + CH2+ + CH+ + C+ + H2O+ + OH+ + O+) with similar mass of cations from methanol. However, Hudson et al. [13] and Djuric et al. [14] have measured the total ionization cross sections for methanol by collecting all fragmentation product simultaneously. For the production of ions CO2+, CO+, O+ and C+ from CO2, Lindsay & Mangan [15], Orient & Srivastava [16] and Crowe & McConkey [17] have reported the partial ionization cross sections. Krishankumar [18] measured the cross sections only for CO2+. Hudson et al. [19] and Rapp & Englander-Golden [20] have measured the total ionization cross sections directly (all fragmentation products are collected simultaneously). Rao & Srivastava [21], Bederski et al. [22], Crowe & McConkey [23] and Mark et al. [24] have investigated experimentally the partial ionization cross sections for production of ions NH3+, NH2+, NH+, H+ and N+ from NH3 while Rejoub et al. [25] have measured the partial ionization cross sections in group of ions NHn+ (NH3+ + NH2+ + NH+ + N+). Recently, Itikawa [10] reported the experimental data of Rejoub et al. [25] for cations from ammonia separately. Theoretical partial ionization cross sections were only calculated by Pal [26] by using Khare-Jain approach for cations from methanol.
Theoretical calculation of ionization cross sections of the molecules by using quantum mechanics is an involved problem even in first born approximation. Hence a number of semi empirical and semi empirical classical formulae have been proposed. Some of these methods are Khare-Jain method [26], Kim-Binary Encounter Bethe (BEB) [27], Khare-Binary Encounter Bethe (BEB) [28], [29], [30], [31], Deutsch-Mark (DM) method [32], complex scattering potential ionization contribution method [33] and Saksena model [34]. As we have seen in literature survey, most of researchers measured the partial ionization cross sections and summed them to obtain the total ionization cross sections. On the other hand, most of theoretical methods provide the total ionization cross sections. Only limited theoretical methods are available to calculate the partial ionization cross sections of cations from molecules due to electron impact. One of successful semi empirical approaches is Khare-Jain method [26]. Khare-Jain method requires Optical Oscillator Strength (OOS), ionization threshold, collisional parameters and mixing parameters to calculate the partial and total cross sections for molecules. Another method was proposed by Saksena et al. [34] but their cross sections are found low at near ionization threshold energies and are greater at intermediate impact energies.
In the present investigation, we have used the Plane Wave Born Approximation (PWBA) and employed the expression of Generalised Oscillator Strength (GOS) given by statistical model of Weizsacker-Williams [35] to calculate the partial ionization cross sections for production of twelve cations (CH3OH+, CH2OH+, CH2O+, CH3+, CH2+, CHO+, CH+, C+, CO+, OH+, H2+ and H+) from methanol, for production of four cations (CO2+, CO+, O+ and C+) from carbon dioxide and for production of five cations (NH3+, NH2+, NH+, N+ and H+) from ammonia molecule. In PWBA, it is well known that the cross sections overestimate the experimental data at low impact energies. This overestimation is supposed to be due to distortion of the incident electron wave function which is the result of electrostatic attractive field of the nucleus of target. This field increases the kinetic energy of incident electron. It is very difficult task to include this effect in theory. To reduce this overestimation in cross sections, we have employed binary encounter theory [28], [35] and multiply cross sections by E/[E + 2I], where E and I are the incident energy and ionization threshold energy (or appearance potential), respectively. The term 2I represents the increase in the kinetic energy of incident electron due to acceleration by the field of target nucleus. Furthermore, we have also modified the Mott term to improve agreement between the theoretical results and experimental data.
Section snippets
Theory
In the Plane Wave Born Approximation (PWBA), the partial ionization cross section, for the production of the jth type ion from a molecule due to electron impact of energy E is given by [28]
In the above equations R, , Fex, Q and w are the Rydberg energy, first Bohr radius, exchange factor, recoil energy and the energy lost by the incident electron in the collision, respectively. The ionization cross section due to the transverse interaction
Result and discussion
We have used the Eq. (4) with Eqs. (8), (9) to calculate partial ionization cross sections of cations produced from methanol, carbon dioxide and ammonia by electron impact ionization. The present model requires only the values of ionization threshold and OOS as input. As for considered molecules, they are taken from Burton et al. [36] and Brion & Thomson [37]. However, the values of OOS for production of ions, are available only up to 80 eV, 80 eV and 60 eV for CH3OH, CO2 and NH3, respectively.
Conclusion
Finally, we conclude that for a successful evaluation of the ionization cross sections a knowledge of Generalised Oscillator Strength (GOS) is not essential. The present method does not need collisional parameters and mixing parameter or other kind of parameter as input, unlike Khare-Jain method [26]. The present cross sections for the production of parent ions and total ionization are found in good agreement with the most of experimental data for all three polyatomic molecules over entire
CRediT authorship contribution statement
Yogesh Kumar: Conceptualization, Methodology, Software. Manoj Kumar: Writing - review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
We are grateful to Ex. professor S.P. Khare, C.C.S. University, Meerut, (India) for fruitful discussion.
References (38)
- et al.
Int. J. Mass Spectrom.
(2016) - et al.
Int. J. Mass Spcctrometry Ion Phys.
(1980) - et al.
Int. J. Mass Spcctrometry Ion Phys.
(1977) - et al.
Chem. Phys. Lett.
(2019) - et al.
Int. J. Mass Spectrom.
(2011) - et al.
Physica B
(1997) - et al.
Chem. Phys.
(1992) - et al.
J. Electron Spectroscopy Related Phenomena
(1984) - S.P. Khare, Introduction to the Theory of Collisions of Electrons with Atoms and Molecules, Klumer Academic Press, New...
- et al.
Phys. Plasmas
(2017)
J. Chem. Phys.
Prog. Energy Combust. Sci.
Ann. Rev. Astronomy Astrophys.
J. Geo. Res.
J. Chem. Phys.
Cited by (7)
Dissociation of Hydrofluorocarbon Molecules after Electron Impact in Plasma
2024, Journal of Physical Chemistry LettersElectron- and positron-driven molecular processes for H<inf>2</inf>O, CO<inf>2</inf>, and NH<inf>3</inf> in their gas and ice phases
2024, Physical Chemistry Chemical PhysicsElectron-impact partial ionisation cross-sections of ethanol
2023, Pramana - Journal of PhysicsElectron impact partial ionization cross sections of 1-butanol
2022, European Physical Journal D