Dissociative Recombination of CH+ Molecular Ion Induced by Very Low Energy Electrons

Zsolt J Mezei,Ousmanou Motapon,Michel D Epée Epée,Ioan F Schneider

doi:10.3390/atoms7030082

Abstract

We used the multichannel quantum defect theory to compute cross sections and rate coefficients for the dissociative recombination of CH + initially in its lowest vibrational level v i + = 0 with electrons of incident energy below 0.2 eV. We have focused on the contribution of the 2 2 Π state which is the main dissociative recombination route at low collision energies. The final cross section is obtained by averaging the relevant initial rotational states ( N i + = 0 , ⋯ , 10 ) with a 300 K Boltzmann distribution. The Maxwell isotropic rate coefficients for dissociative recombination are also calculated for different initial rotational states and for electronic temperatures up to a few hundred Kelvins. Our results are compared to storage-ring measurements.

Highlights

The methylidyne cation CH+ is one of the most important molecular species for astrophysical observations having a particular interest for the formation of large hydrocarbons in the interstellar medium (ISM)
We use an Multichannel Quantum Defect (MQDT)-type method to study the electron-impact collision processes given by Equations (1) which result from the quantum interference of the direct mechanism—the capture takes place into a dissociative state of the neutral system (CH∗∗ )—and the indirect one —the capture occurs via a Rydberg state of the molecule CH∗ which is predissociated by the CH∗∗ state
The molecular data necessary to model the dissociative recombination and rotational excitation are the potential energy curve (PEC) of the ground state of the ion, the PECs of the neutral valence dissociative states interacting with the ionization continua, those of the Rydberg states associated to these continua below the threshold and all the relevant Rydberg-valence couplings

Summary

Introduction

The methylidyne cation CH+ is one of the most important molecular species for astrophysical observations having a particular interest for the formation of large hydrocarbons in the interstellar medium (ISM). Calculation of DR was performed by Carata et al [13] where they took into account the effect of core excited states Their result have reproduced the broad resonances mentioned by Amitay et al but they have underestimated the experimental data by more than an order of magnitude, especially at higher collision energies. This was followed by the study of Guberman [14] on the angular distributions of the products of dissociative recombination of CH+.

Theoretical Method

Cross Sections and Rate Coefficients

Conclusions