Electron-impact cross sections for dissociation processes of vibrationally excited CH radical

TL;DR

This work addresses the lack of vibrationally resolved electron-impact cross sections for dissociative attachment and dissociative excitation of vibrationally excited CH. It combines ab initio $R$-matrix theory for CH and CH$^-$ resonances with a Local Complex Potential treatment of nuclear motion to compute cross sections and rate coefficients for DA and DE across CH's low-lying electronic states. The study introduces CH$^-$ resonant states, constructs high-quality potential energy curves with MRCI, and delivers vibrationally resolved cross sections and Maxwellian rate coefficients, highlighting oscillatory structures arising from resonant dynamics. The resulting data, available in the LXCat database, have direct implications for modeling non-equilibrium CH-containing plasmas in CO$_2$ reduction, combustion, and various astrophysical environments.

Abstract

This paper presents a theoretical investigation of the cross sections for dissociative electron attachment and dissociative excitation processes in vibrationally excited CH radicals induced by electron impact. Resonant electron-CH collisions are analyzed using the ab-initio R-matrix method, while nuclear dynamics are explored within the Local Complex Potential framework. A comprehensive set of vibrationally resolved cross sections and rate coefficients is provided for both the ground and first excited electronic states of the CH molecule. These findings contribute to a better understanding of the kinetics of non-equilibrium systems containing CH molecules with applications in plasma technologies for CO2 reduction, combustion processes and various astrophysical contexts.

Figures (7)

• Figure 1: Eigenphase sum for the symmetries $^1\Sigma^+$, $^3\Pi$ and $^5\Sigma^-$ of the CH$^-$ system calculated at CH equilibrium distance.
• Figure 2: (Top) Potential energy curves for the two low-lying electronic states of CH radical (solid blue lines) as obtained by MRCI approach and for the CH$^-$ anionic states (broken lines) as obtained from $R$-matrix~ calculations. (Bottom) Widths of the CH$^-$ resonances considered in the text. Filled circles represent the calculated $R$-matrix~ results.
• Figure 3: Real and imaginary part of the resonant wave function $\xi^1_{0,v}(R)$ for a collision of CH$(\mathrm{X}\,^2\Pi, v=0)$ (plot on the left) and CH$(\mathrm{X}\,^2\Pi, v=10)$ (plot on the right) with an electron of energy $\epsilon=5$ eV. Initial vibrational wave functions of CH molecule and the classical turning point $R_E$ are also shown. Amplitudes are not to scale.
• Figure 4: Cross sections for the DA and DE processes from the ground state $\mathrm{X}\,^2\Pi$ of CH molecule for the vibrational levels $v=0,5,10,16$.
• Figure 5: Cross sections for the DA and DE processes from the excited state $a\,^4\Sigma^-$ of CH molecule for the vibrational levels $v=0,5,11$.