Optimization of the infrared multiple-photon dissociation of SiF 4 to increase the isotopic selectivity

Abstract

The influence of laser fluence and wavelength as well as of the sample pressure on the infrared multiple-photon dissociation (IRMPD) of SiF4 and H2 mixtures has been studied. Different lines of the 9.4 μm emission band of a TEA CO2 laser have been used as excitation sources. A power law dependence of the fraction of molecules dissociated per pulse on the laser fluence was found. The optimization of the IRMPD of silicon tetrafluoride was performed by varying both SiF4 and H2 pressures. The IRMPD spectrum exhibits a red shift of ∼ 12 cm-1 produced by the anharmonicity of the molecular vibrations. Moreover, the isotopic selectivity of the IRMPD of SiF4 has been determined with wavelengths shifted to the red and the blue of the 9P(36) line which is quasi-resonant with the v3 mode of 28SiF4. The maximum values were obtained with the 9P(32) emission line which has the least overlap with the absorption bands of the less abundant species.