Alteration of Cl spin-orbit branching ratios via photodissociation of pre-excited fundamental CH₃ stretch of CH₃CFCl₂

The fundamental symmetric CH₃ stretch (ν₂) in the ground electronic state of CH₃CFCl₂ is efficiently prepared by stimulated Raman excitation. The excited molecules are photodissociated by ~235 nm photons that further tag Cl(²P_3/2) and Cl(²P_1/2) [Cl^*] photofragments via (2+1) resonantly enhanced multiphoton ionization. The yield of both photofragments increases as a result of pre-excitation, indicative of energy flow from the excited C-H to the C-Cl bond and hence a better Franck-Condon overlap between the components of the wavefunction along the C-Cl coordinate. The Cl^*/Cl branching ratio is 0.60±0.09 in ~235 nm photolysis of vibrationally excited molecules and 0.40±0.07 in that of vibrationless ground state CH₃CFCl₂.