Competition between radiative and predissociative decay mechanisms in excited electronic states of CH radical

Abstract

The CH radical is an important astrophysical molecule due to its ubiquity in the universe, and its relatively low dissociation threshold leads to manifestations of photodissociation and predissociative behaviour at low photon energies. This study investigates the competition between radiative decay and predissociation in three excited electronic states of the CH radical, A ²Δ, B ²Σ⁻, and C ²Σ⁺. The predissociation processes are modelled using a combination of the stabilization approach based on rigorous solutions of the Shrödinger equation using code Duo, and WKB-type approach using code LEVEL to describe Feshbach and tunnelling resonances, respectively. Total lifetimes compare favourably with experimental data for A ²Δ and C ²Σ⁺ states, but our B ²Σ⁻ predictions are understimated above the dissociation threshold. The predissociative lifetimes for levels belonging to A ²Δ and C ²Σ⁺ states are often found to be comparable to their radiative lifetimes. These weak predissociation effects in A ²Δ and C ²Σ⁺ states and coupling mechanisms responsible for them are discussed.