Cross Sections and Rate Coefficients for Rotational Excitation of HeH+ Molecule by Electron Impact

Marjan Khamesian,Mehdi Ayouz,Jasmeet Singh,Viatcheslav Kokoouline

doi:10.3390/atoms6030049

Abstract

Cross sections for rotational excitation and de-excitation of the HeH+ ion by an electron impact are computed using a theoretical approach that combines the UK R-matrix code and the multi-channel quantum defect theory. The thermally-averaged rate coefficients derived from the obtained cross sections are fitted to an analytical formula valid for a wide range of temperatures.

Highlights

Cross sections for the electronic, rotational, and vibrational excitation of molecules in collisions with electrons are important for understanding and modeling various plasma environments, such as the interstellar medium (ISM), planetary ionospheres and exospheres, in plasma processing and de-pollution technologies, and others
The first-order perturbation theory was applied, and a general analytical formula was derived in which dipole and quadrupole moments of the target ion determine the cross section for rotational excitation, while derivatives of the moments with respect to nuclear distances determine the cross section for vibrational excitation
The theoretical method accounts for near-threshold effects, including rovibrational Rydberg resonances, and makes use of first-principle calculations, and is based on (1) the electron–molecule scattering matrix computed for fixed positions of nuclei, (2) the idea of the rotational frame transformation [11], and (3) the molecular quantum defect theory (QDT) [12,13], which makes it possible to evaluate the scattering matrix in the laboratory frame and excitation cross sections

Summary

Introduction

Cross sections for the electronic, rotational, and vibrational excitation of molecules in collisions with electrons are important for understanding and modeling various plasma environments, such as the interstellar medium (ISM), planetary ionospheres and exospheres, in plasma processing and de-pollution technologies, and others. The theoretical method accounts for near-threshold effects, including rovibrational Rydberg resonances, and makes use of first-principle calculations (or experimental spectroscopic data if necessary), and is based on (1) the electron–molecule scattering matrix computed for fixed positions of nuclei (molecular-frame scattering matrix), (2) the idea of the rotational frame transformation [11], and (3) the molecular quantum defect theory (QDT) [12,13], which makes it possible to evaluate the scattering matrix in the laboratory frame (with respect to which the molecule rotates) and excitation cross sections. In Appendix A, details of the theoretical derivation of the main formulas of Section 2 are provided

Theoretical Approach

Cross Sections and Rate Coefficients

Conclusions