PHOTOABSORPTION, PHOTOIONIZATION, AND NEUTRAL-DISSOCIATION CROSS-SECTIONS OF SIF4, SICL4, AND SI(CH3)4 IN THE EXTREME-ULTRAVIOLET RANGE

The absolute photoabsorption cross sections (sigma(t)) and photoioniza tion quantum yields (eta) of SiF4, SiCl4, and Si(CH3)4 have been measu red in the 50-100 nm range, from which we have evaluated the absolute photoionization cross sections (sigma(i)) and the total cross sections for nonionizing processes, i.e., the neutral-dissociation cross secti ons (od) following superexcitation. In addition to the broad structure s in the sigma(t) curve for SiF4 around 95, 83, 78, 74.5, and 70 nm, o scillating structures which have not been found previously are reveale d around 65 nm. These structures, which appear also in the present sig ma(i) curve, are tentatively ascribed to the vibrational progressions of Rydberg states converging to the (4t2)-1C ionic state. Other oscill ating structures in the 57-62 nm range are ascribed to the Rydberg sta tes converging to the (5a1)-1D ionic state. Broad peaks around 95, 92, 75, and 58 nm are observed in the sigma(t) and sigma(i) curves Of SiC l4. Rydberg structures converging to the 7a1(-1) limit are observed in the sigma(t) and sigma(i) curves in the 68-74 nm range. A general app earance of the cross sections of Si(CH3)4 resembles that of CH4.