Mechanism of the ultraviolet photodissociation of chloroethylenes determined from the Doppler profiles, spatial anisotropy, and power dependence of the photofragments.

Doppler profiles of chlorine and hydrogen atomic fragments produced in the photodissociation of mono- and dichloroethylenes at 193 nm have been measured in a pump-and-probe experiment using 2+1 resonance-enhanced multiphoton ionization. In a second experiment, the angular distributions of the Cl fragments produced from chloroethylenes at 235 and 238 nm were measured using a perfect-focusing mass spectrometer. In a third experiment, we measured the power dependence of the relative yields of H, Cl, HCl, and HCl+ produced from vinyl chloride at 193 nm. For Cl detachment, two primary processes have been confirmed. One produces an isotropic angular distribution of photofragments, while the other produces an anisotropic distribution. For H atom detachment, an isotropic angular distribution and a Boltzmann velocity distribution were found. The ratio of yields of the Cl and H fragments was found to be 4±1 for CH2CCl2 and higher than 10 for t-CHClCHCl and CCl2CClH. The H, Cl, and HCl yields were found to be first order in laser intensity, while the HCl+ yield was found to be third order. Saturation measurements of the ion yield indicate that the latter results from a 1+1+1 resonance-enhanced process involving a bound state of the parent molecule. This intermediate state may also be responsible for producing the statistical component of the Cl atom product. [ABSTRACT FROM AUTHOR]