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(2P3/2) and Cl(2P1/2) [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.