Effective cross sections and rates coefficients derived from collision-induced rotational excitation of HCl\(^{+}(X^{2}\Pi )\) with He(\(^{1}S\)): isotopic effects

Abstract

In this work, we studied the helium-induced collisional excitation of the radical ion HCl⁺. Our work focuses on calculating two-dimensional potential energy surfaces (PES) to study the interaction due to the collision between HCl⁺ and He, and on analyzing the influence of the isotopic effect on cross sections and collision rates. For Ab initio calculations of PES \(^{2}A^{\prime }\) and \(^{2}A^{\prime \prime }\) of HCl⁺(X\(^{2}\Pi \))-He complex, we used the RCCSD(T)-F12 method with cc-pVQZ-F12 basis sets. These surfaces have been fitted using the Reproducing Kernel Hilbert Space (RKHS) method and were submitted to the close-coupling approach in order to work out the inelastic integral cross sections. Collision cross sections taking into account the fine structures of HCl⁺ have been performed for kinetic energies up to 3500 cm⁻¹ and the thermal excitation rates for kinetic temperatures varying from \(4K\) up to 400 K. It appears that the difference in the cross section and collisional rate cofficients for the H³⁵Cl⁺ and H³⁷Cl⁺ colliding with He was found to be negligeable. In contrast, a significant difference in effective cross-sections and collision rates between HCl⁺-He and DCl⁺-He was observed to the extent that it is impossible to make estimation of collision rates of deuterated species from those of the hydrogenated species.