Infrared laser photochemistry of silane-chloromethane mixtures

By use of a pulsed CO{sub 2} TEA laser at 944.19 cm{sup {minus}1} and fluences in the range of 0.49-0.71 J/cm{sup 2}, the infrared photochemistry of SiH{sub 4}-CH{sub 3}Cl mixtures has been studied in a pressure range of 50-100 Torr and over a temperature range of 295-428 K. The gaseous products observed are H{sub 2}, CH{sub 4}, Si{sub 2}H{sub 6}, and SiH{sub 3}Cl, with trace amounts of Si{sub 3}H{sub 8} and perhaps CH{sub 3}SiH{sub 2}Cl. As is usual in silane decomposition, a brown solid product containing silicon, hydrogen, and, under some conditions, chlorine was also produced. The photochemical conversion is best described by initial decomposition of SiH{sub 4} to SiH{sub 2} and H{sub 2} followed by competition of SiH{sub 4} and CH{sub 3}Cl for SiH{sub 2} molecules. The production of CH{sub 4} is believed to occur via the decomposition of highly energized CH{sub 3}SiH{sub 2}Cl* (formed by SiH{sub 2} insertion into the C-Cl bond of CH{sub 3}Cl), yielding CH{sub 4} and SiHCl as products. SiH{sub 3}Cl is then formed by the secondary reaction of SiHCl with SiH{sub 4}.