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

The fundamental symmetric CH3 stretch (nu(2)) in the ground electronic stat e of CH3CFCl2 is efficiently prepared by stimulated Raman excitation. The e xcited molecules are photodissociated by similar to 235 nm photons that fur ther tag Cl(P-2(3 / 2)) and Cl(P-2(1 / 2)) [Cl*] photofragments via (2 + 1) resonantly enhanced multiphoton ionization. The yield of both photofragmen ts 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 b etween the components of the wavefunction along the C-Cl coordinate. The Cl */Cl branching ratio is 0.60 +/- 0.09 in similar to 235 nm photolysis of vi brationally excited molecules and 0.40 +/- 0.07 in that of vibrationless gr ound state CH3CFCl2. (C) 1999 Elsevier Science B.V. All rights reserved.