Mass spectrometric study of the mercury-photosensitized reactions of silane and methylsilane with nitric oxide

Abstract

Silyl radicals and methylsilyl radicals formed by Hg (63Pi)-photosensitized decomposition of silane and methylsilane, respectively, react efficiently with nitric oxide to produce siloxanes and nitrous oxide as the principal products. The reaction is a chain reaction at room temperature which, from the evidence at hand, is proposed to involve SiH80(SiH20)" and CH3SiH20(CH3SiH0)" radicals, in = 0,1, 2, .. .), as well as the primary radicals SiH8 and CH3SiH2.It has previously been reported from this laboratory that, when nitric oxide at low concentration is employed at room temperature as a scavenger of methyl radicals, trimethylhydroxylamine is the stable product of the radical-scavenging process and is formed by the successive addition of methyl radicals to nitric oxide.2•8 Recent studies of the mercury-photosensitized decomposition of monosilane4•5 have suggested that the formation of the predominant silicon-containing product, disilane, may occur via the combination of silyl radicals, viz. SiH3 + SiH3 -> Si2He(1) and, in this respect, at least, may resemble mechanistically the analogous ethane formation in systems containing methyl radicals. However, despite this sim-

Free-radical chain formation of siloxanes in the radiolysis of monosilane-nitric oxide mixtures

“…The slope in Figure 5 yields the rate constant ratio ku/kw = 3,6. In accord with our assumption in reducing ( 22) to ( 23), a similar value is expected for the ratio kw/ku, It is somewhat surprising to find the H abstraction from SiH4 (10) to be only about 4 times slower than the addition reaction to NO, (11), but this is, in our opinion, the most reasonable interpretation of the results. This conclusion implies that the bond-dissociation energy D(SiH3OSiH2-H) is probably significantly greater than the 89 ± 4 kcal/mol reported for D(SiH3-H).29 100-eV yield of Si2H6 is reduced to the average plateau value (i.e., complete radical scavenging) of 2.9 at all concentrations of NO employed.…”

“…H3SiOSiH2• + NO -> H3SiOSiH2ON (11) H3SiOSiH2ON + NO -» H3Si0SiH20• + N20 (12) H3Si0SiH20• + SiH4 -> H3SiOSiH2OSiH2-+ H2 (13) H3SiOSiH2OSiH2• + SiH4 -> H3SiOSiH2OSiH3 + SiH, ( 14)…”

Photochemistry of silicon compounds. 6. The 147-nm photolysis of tetramethylsilane

“…From the results it is estimated that at least about 15% of the hydrogen arises from molecular elimination (CH3)4Si -^H2 + CHSi(CH3)3 (41) and the rest from atomic hydrogen via abstraction…”

Mercury‐sensitized photochemical vapor deposition of amorphous silicon

“…The Hg* atom is 469.4 kJ/mol above the ground state (Calvert and Pitts, 1966). This excess energy can be transferred to the silane and hydrogen via collision, leading to the generation of SiH, and H radicals and the quenching of Hg* back to the ground state (Niki and Mains, 1964;Yarwood et al, 1964;Kamaratos and Lampe, 1970). H radicals formed by the reaction of Hg* with silane and hydrogen can further react with silane to form SiH, radicals and molecular hydrogen (Austin and Lampe, 1977).…”