Dynamics of vibrationally mediated photodissociation of CH3CFCl2

The similar to 235 nm photodissociation of CH3CFCF2 pre-excited to three, f our, 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-bod y 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-arriva l profiles revealed their energies and angular distributions and showed bro ad and unstructured fragment kinetic energy distributions. Although a signi ficant amount (similar to 50%) of the available energy is transferred into internal energy of the CH3CFCl fragment, the spatial Cl distribution is cha racterized by a nonvanishing anisotropy parameter, beta, which indicates at a fast dissociation of the parent molecule along the C-Cl dissociation coo rdinate. Moreover, beta for Cl changes from a slightly positive value to a negative value, while that for Cl* increases when the pre-excitation is inc reased from three to five quanta of C-H methyl stretches. This is attribute d to the promotion of one of the nonbonding electrons located on the Cl ato ms to the sigma* antibonding C-Cl orbital and involvement of several upper states with different symmetry properties. (C) 2001 American Institute of P hysics.