Chemical and Electronic Branching Ratios in the Chemiluminescent Reactions of Hyperthermal Ca(3P) Atoms with CF2Cl2 and CF2CCl2

Abstract

Chemiluminescent reactions of hyperthermal Ca( 3 P) with CF 2 Cl 2 and CF 2 =CCl 2 were studied in a beam-gas arrangement under single collision conditions. Emissions associated with the A( 2 Π Ω ) → X( 2 Σ + ) and the B( 2 Σ + ) → X( 2 Σ + ) transitions from CaCI and CaF were observed for both reactions. The chemical and electronic branching ratios were determined for these reactions, and different results were obtained for each one. The different behavior was rationalized by a simple MO pictures. For the case of the reaction with CF 2 Cl 2 it was assumed that an electron from Ca( 3 P) is transferred to a σ*(C-Cl) orbital in CF 2 Cl 2 which, at higher translational energies can also enter into a σ*(C-F) orbital of the same molecule. In both cases the molecular anion produced is short-lived and will undergo fast decay to Cl - or F - to yield CaCl and CaF. For the reaction with CF 2 =CCl 2 the electron from Ca( 3 P) is transferred to a π* orbital of the reagent molecule that generates a relatively stable molecular anion with 2 Π symmetry. This anion subsequently cross over several repulsive 2 Σ surfaces associated with σ* orbitals of the C-Cl and the C-F bonds, to dissociate into Cl - or F - to produce CaCI and CaF. The electronic branching ratios are in good agreement with statistical distribution based on information theory approach, assuming the rigid rotor harmonic oscillator (RROH) approximation for the reaction with CF 2 Cl 2 and the formation of a collision complex for the reaction with CF 2 =CCl 2 .