Journal of Chemical Physics, Vol.115, No.14, 6418-6425, 2001
Dynamics of vibrationally mediated photodissociation of CH3CFCl2
The similar to 235 nm photodissociation of CH3CFCF2 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 similar to 235 nm photons also tagged spin-orbit ground (ClP3/2)-P-2 [Cl] and excited Cl(2)p(1/2) [Cl*] state photofragments, via (2+1) resonantly enhanced multiphoton ionization in a time-of-flight mass spectrometer. Monitoring the shapes of Cl-35 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 (similar to 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, beta, which indicates at a fast dissociation of the parent molecule along the C-Cl dissociation coordinate. Moreover, beta 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 sigma* antibonding C-Cl orbital and involvement of several upper states with different symmetry properties.