Dynamics of vibrationally mediated photodissociation of CH3CFCl2

Abstract

The ∼235 nm photodissociation of CH3CFCl2 pre-excited to three, four, and five quanta of C–H methyl stretches was studied to investigate the effect of internal parent excitation on the dynamics of two- and three-body photofragmentation. The ∼235 nm photons also tagged spin-orbit ground Cl 2P3/2 [Cl] and excited Cl 2P1/2 [Cl*] state photofragments, via (2+1) resonantly enhanced multiphoton ionization in a time-of-flight mass spectrometer. Monitoring the shapes of Cl35 and Cl*35 time-of-arrival profiles revealed their energies and angular distributions and showed broad and unstructured fragment kinetic energy distributions. Although a significant amount (∼50%) of the available energy is transferred into internal energy of the CH3CFCl fragment, the spatial Cl distribution is characterized by a nonvanishing anisotropy parameter, β, which indicates at a fast dissociation of the parent molecule along the C–Cl dissociation coordinate. Moreover, β for Cl changes from a slightly positive value to a negative value, while that for Cl* increases when the pre-excitation is increased from three to five quanta of C–H methyl stretches. This is attributed to the promotion of one of the nonbonding electrons located on the Cl atoms to the σ* antibonding C–Cl orbital and involvement of several upper states with different symmetry properties.