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

## TL;DR

This paper studies how the CH radical in excited states can either emit light or break apart, comparing these processes using theoretical models.

## Contribution

The study introduces a combined stabilization and WKB-type approach to model predissociation in CH radical excited states.

## Key findings

- Predissociation lifetimes in A 2Δ and C 2Σ+ states are comparable to radiative lifetimes.
- B 2Σ− state predictions are underestimated above the dissociation threshold.
- Weak predissociation effects occur in states with long radiative lifetimes and weak couplings.

## 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.

Levels in excited electronic states with weak couplings and long radiative lifetimes can show weak predissociation, and molecules in those states are as likely to emit a photon as to break apart.