Electron–molecule collisions with explicit rovibrational resolution at MRCI level and using even tempered basis sets

Abstract

A method for calculating the generalized oscillator strengths (GOSs) and differential cross section (DCS) with vibration and rotation resolution is presented. The importance of accounting for the rotational contribution is to be emphasized since it has not previously been considered in GOS calculations. Although largely neglected due to its small effect on various properties, the rotational resolution proved to be fundamental in the study of certain phenomena, such as the interference between rotational states in a molecule. As the general goal of this work is to obtain theoretical values comparable to high resolution experiments, special care was taken on the calculation of the electronic part of the scattering amplitude, particularly in what concerns the choice of the atomic basis set. Accordingly, even-tempered basis sets have proved to lead to good results. The helium atom was taken as a model system for this aspect of the problem. Then, GOS and DCS, for explicit vibrational and rotational transitions, were calculated for hydrogen and nitrogen molecules. For higher accuracy, a non-Franck–Condon approach was used to obtain transitions involving vibrational states. The resultant values have shown good agreement with the available experimental data.

Theoretical Study of Valence Shell Excitation by Electron Impact in CCl4

“…Besides, (4π) −1 ∫ dΩ K is the spherical averaging, which is required for taking into account the random orientation of the gaseous molecules . While an alternative integration over molecular orientation with rovibrational resolution has recently been used to calculate the GOS profiles of diatomic molecules by Oliveira et al, it is not applicable to the present calculations. If M n 0 ( K , Q ) is practically independent of Q within the Franck–Condon region, eq can be approximated as f 0⃗ → n ( K ) = 2 E n 0 K 2 M n 0 ( K , Q 0 ) where Q 0 is the nuclear coordinate at the equilibrium geometry.…”