Photodissociation of Chlorine Molecules Adsorbed on Amorphous and Crystalline Water Ice Films

Abstract

The photodissociation dynamics of chlorine molecules adsorbed on amorphous and crystalline water ice films was investigated at 351 nm. The ice films were prepared on a gold polycrystalline substrate at 80−140 K. Time-of-flight spectra of the photofragment chlorine atoms, measured with the resonance-enhanced multiphoton ionization technique, were simulated with a composite of two translational energy distributions: a Gaussian distribution and a flux-weighted Maxwell−Boltzmann distribution. For both amorphous and crystalline ice films, the Gaussian distribution is characterized by the average energy 〈Et〉 = 0.38 ± 0.02 eV, while the Maxwell−Boltzmann one by 〈Et〉 = 0.12 ± 0.01 eV. The Gaussian distribution is attributable to the chlorine atoms produced from the direct photodissociation of Cl2, while the Maxwell−Boltzmann characterizes those having undergone strong relaxation processes. The observed translational energy distributions for amorphous and crystalline ice films were similar to each other, but the ...