Reaction kinetics of alkylsilylenes (R = butyl, pentyl, and methylpentyl) and silacyclopropane intermediates produced by silylene additions to 1-butene, 1- and 2-pentene, 2-methyl-1-pentene, and 4-methyl-1-pentene are reported. Observations are consistent with a homogeneous, Barton2-type mechanism, which describes alkylsilylene isomerization and decomposition in terms of silacyclopropane (SCP) intermediates. Modeling studies on this basis conclude that SCP-forming and -opening reactions are at least an order of magnitude faster than SCP decompositions to olefins and SiH2. All reactions are pressure dependent at 400 Torr. Decomposition versus trapping comparative rate data at 410 Torr, based on butylsilylene- and pentylsilylene-trapping reactions with silane of 4.8 x 10(9) M-1 s-1 and 3.1 x 10(9) M-1 s-1, respectively, give limiting high-pressure Arrhenius parameters for the butyl- and pentylsilylene decompositions of log A infinity = 15.5 +/- 0.1, E infinity = 22.5 +/- 0.3 kcal. The activation energies are consistent with the decomposition reaction thermochemistries (DELTA-H(dec) = 26.6 +/- 3.4 kcal, DELTA-E(dec) = 25.3 +/- 3.4 kcal), and A factors indicate surprisingly loose transition states for both alkysilylene decompositions as well as their reverse silylene/olefin additions. A loose silylene/olefin addition complex is suggested for the transition state as the thermochemistry of decomposition precludes the intermediacy of biradicals. Generic high-pressure Arrhenius parameters (A, s-1: E, kcal) are deduced for silacyclopropane ring-opening (o), -closing (c), and -decomposition (d) reactions: log A(c) = 12.3, E(c) = 10.4; log A(o) = 14.0, E(o) = 14.7 + DELTA-E; log A(d) = 16.9, E(d) = 26.1 + DELTA-E, where DELTA-E = (49.6 - SCP strain energy). The low SCP ring-closing activation energy indicates zero ring strain development in the transition state and is consistent with a reanalysis of prior estimates of the activation energy of the SiH2 + CH4 strain free, C-H bond insertion reaction.
Diagnostics of the gas-phase thermal decomposition of Si2H6 using vacuum ultraviolet photoionization
作者:Kenichi Tonokura、Tetsuya Murasaki、Mitsuo Koshi
DOI:10.1016/s0009-2614(00)00165-2
日期:2000.3
Vacuum ultraviolet (VUV) photoionization at 10.2 eV was employed for the detection of gas-phase molecules formed after thermal decomposition of disilane at a total pressure of 30 Torr and in the temperature range of 298–740 K. The SinH2(n+1) (n=3–5) and SinH2n (n=2–5) species resulting from disilane pyrolysis in a flow reactor were directly observed using time-of-flight mass spectrometry. Unlike multiphoton
在10.2 eV的真空紫外(VUV)光电离被用于检测乙硅烷在30 Torr的总压力和298–740 K的温度范围内热分解后形成的气相分子。Si n H 2(n使用飞行时间质谱法直接观察到在流动反应器中乙硅烷热解产生的+1)(n = 3-5)和Si n H 2 n(n = 2-5)物质。与在6.4 eV光子下的多光子电离不同,在10.2 eV的VUV单光子电离没有观察到碎片。
Shock-induced kinetics of the disilane decomposition and silylene reactions with trimethylsilane and butadiene
作者:J. Dzarnoski、S. F. Rickborn、H. E. O'Neal、M. A. Ring
DOI:10.1021/om00069a020
日期:1982.9
VUV photoionization time-of-flight mass spectrometry of flash pyrolysis of silane and disilane
作者:Steven D. Chambreau、Jingsong Zhang
DOI:10.1016/s0009-2614(01)00739-4
日期:2001.8
Flash pyrolysis of silane, SiH4, and disilane, Si2H6, diluted in He or Ar (1%), was carried out at temperatures ranging from similar to 700 to similar to 1500 K. After a short reaction time of similar to 20 mus, the initial products were isolated in a supersonic molecular beam and detected by single vacuum ultra-violet (VUV) photon (lambda = 118 or 121 nm) ionization time-of-flight mass spectrometry (TOFMS). Initial decomposition and reaction products, both free radical intermediates and stable species, were directly observed, which included SiH2 and Si2H4. (C) 2001 Elsevier Science B.V. All rights reserved.