Photolysis and desorption of adsorbed halomethane molecules under long-wavelength radiation of excimer lasers

Abstract

The photolysis and desorption of CH2I2, CH3I, CCl4, CHCl3, CH2Cl2, CF2Cl2, and CHF2Cl molecules adsorbed on fused silica under the action of XeF and XeCl laser radiation absorbed by these molecules have been studied. The desorption of molecules that occurs due to expansion to the long-wavelength region of the absorption spectrum of molecules in the adsorbed state, compared to the gas phase, predominates. The laser desorption is characterized by a strong nonlinear dependence on the density of radiation energy. Depending on the relationship between the laser radiation wavelength and the spectrum of electronic states of molecules, photolysis is observed upon absorption of either one or two photons. At an increased fluence of laser radiation energy, the one-photon detachment of the primary CH2I fragment from the CH2I2 molecule changes into the three-photon process. A similar behavior is revealed for the desorption of CH3I molecules from clusters formed on the surface in multilayer adsorption coverages.