Theoretical study of valence excitations in CFCl3 and CF2Cl2 on the basis of generalized oscillator strengths

Abstract

This paper presents a theoretical investigation into the electron excitations of CFCl₃ and CF₂Cl₂, whose photolysis results in the release of chlorine atoms, causing the destruction of stratospheric ozone. The generalized oscillator strengths (GOSs) of valence excitations are calculated at the equation-of-motion coupled-cluster singles and doubles level. The results for electron excitations from Cl 3p nonbonding orbitals (n_3p) to the lowest-lying C-Cl antibonding orbital (σ^⁎) show overall reasonable agreement with the available experimental data. Furthermore, the calculations demonstrate that excitations to the second lowest C-Cl antibonding orbital considerably contribute to the energy region of 8.5–9.5 eV. It is also shown that the C-Cl asymmetric stretching vibration exerts a notable influence on several valence excitations. Additionally, the effect of successive chlorination on the GOS profiles for a series of chlorofluoromethanes is examined to acquire a comprehensive understanding of n_3p → σ^⁎ transitions observed in a range of chlorofluorocarbons and hydrochlorofluorocarbons.