Photochemistry of CF₃Cl: Quenching of Charged Fragments Is Caused by Nonadiabatic Effects

Abstract

For the first time, high-level multireference electronic structure calculations have been performed to study the photochemistry of CF₃Cl, allowing a comprehensive interpretation and assignment of experimental data concerning fluorescence, ion-pair formation, and generation of CF₃ fragments in several electronic states. All studied dissociation channels correlate either with Cl or Cl^- in the ground state. On the other hand, a CF₃ fragment can be generated either in the ground or excited state. A rationalization for the nonadiabatic relaxation of CF₃Cl, including the formation of an (n4s) stable state and internal conversion at multiple-state intersections, has been provided. Our results explain the anomalous quenching of a charged fragment after low-energy excitation, a fact experimentally observed by separate groups. We show that the CF₃⁺···Cl^- ion pair undergoes an internal conversion to the ground state, producing neutral CF₃ and Cl fragments. The results also allow understanding as to why CF₃Cl is usually a nonemitting species and how UV emission could be induced.