Abstract:

The photodissociation dynamics of chloroiodomethane in the A-band has been investigated by ion velocity imaging coupled with a resonance enhanced multiphoton ionization (REMPI) scheme. Translational energies and angular distributions of the corresponding photofragments were obtained by detecting ion images of I*(5p 2P1/2) and I (5p 2P3/2) at 266 and 277 nm. Single-peaked Gaussian translational energy distributions were found for I and I* and could be interpreted in terms of the soft radical approximation. The formation of I and I* took place via a fast direct dissociation process on a repulsive potential energy surface. The obtained anisotropy parameter β proved that the existence of a nonadiabatic transition between the 3Q0 and 1Q1 states, and excitation at these wavelengths was predominated to the 3Q0 state. The nonadiabatic transition between the 3Q0 and 1Q1 states is stronger at shorter wavelengths. Around 235 nm, the isotropic Cl and Cl*ion images suggest that the observed chlorine atoms come from the secondary UV photodissociation of CH2Cl radicals which are initially produced by the photodissociation of CH2ICl.

Key words: Photodissociation, Ion velocity imaging, Chloroiodomethane, Secondary photodissociation process