Ab Initio Diabatic Potential Energy Matrix for the Lowest-lying Singlet States of HCN Responsible for Collisional Excitation/Quenching of CN(X2Σ+/A2Π) with H

Abstract

In hyperthermal chemistry, eElectronically excited cyano radicals (CN) are considered as a key radiative source in hyperthermal chemistry in the shock boundary layer in front of supersonic (re)entry vehicles. To correctly model the radiative heating in such extreme environments, it is necessary to understand collisional excitation and quenching rates. Although quenching of CN(A2Π) to CN(X2Σ+) with various collision partners has been investigated experimentally, a quantitative understanding of the nonadiabatic transitions in such electronically inelastic scattering has not been achieved. In this work, a full-dimensional diabatic potential energy matrix (DPEM) for the three lowest-lying singlet A′ states of HCN, namely the 1 1 A′, 2 1 A′, and 3 1 A′ states, are developed based on multi-reference configuration interaction calculations. The DPEM provides valuable insights into the quenching/excitation of CN(X2Σ+/A2Π) via collisions with H in the singlet manifold.