Infrared multiphoton decomposition of phosphine sensitized by silicon tetrafluoride

Abstract

The decomposition of PH/sub 3/, sensitized by the multiphoton absorption of unfocussed infrared laser radiation by SiF/sub 4/, has been studied in the fluence range of 0.2-0.6 J/cm/sup 2/ and over a total pressure range of 1-16 torr. Absorption of radiation at 1025.3 cm/sup -1/ results in the formation of H/sub 2/ and a solid deposit which is probably composed of polymeric phosphorus hydrides of formula (PH)/sub x/. No significant amount of gaseous phosphorus compounds were detected, although it is possible that trace amounts of P/sub 2/(g) were formed. The effects of initial composition, pressure, fluence, and presence of foreign gases (He, N/sub 2/) on the yields of PH/sub 3/ decomposition and H/sub 2/ formation were examined. A mechanism is proposed which involves absorption of laser energy by SiF/sub 4/, followed by collisional energy transfer to PH/sub 3/ and subsequent unimolecular decomposition of PH/sub 3/ to PH and H/sub 2/. The mechanism is shown to be in reasonable accord with the experimental data.