Becerra Rosa, Cannady J Pat, Dormer Guy, Walsh Robin
Instituto de Quimica-Fisica Rocasolano, C.S.I.C., C/Serrano 119, 28006 Madrid, Spain.
J Phys Chem A. 2008 Sep 18;112(37):8665-77. doi: 10.1021/jp803391g. Epub 2008 Aug 21.
Time-resolved kinetic studies of the reaction of dideutero-silylene, SiD 2, generated by laser flash photolysis of phenylsilane-d 3, have been carried out to obtain rate constants for its bimolecular reaction with C 2H 2. The reaction was studied in the gas phase over the pressure range 1-100 Torr in SF 6 bath gas, at five temperatures in the range 297-600 K. The second-order rate constants obtained by extrapolation to the high-pressure limits at each temperature fitted the Arrhenius equation log( k (infinity)/cm (3) molecule (-1) s (-1)) = (-10.05 +/- 0.05) + (3.43 +/- 0.36 kJ mol (-1))/ RT ln 10. The rate constants were used to obtain a comprehensive set of isotope effects by comparison with earlier obtained rate constants for the reactions of SiH 2 with C 2H 2 and C 2D 2. Additionally, pressure-dependent rate constants for the reaction of SiH 2 with C 2H 2 in the presence of He (1-100 Torr) were obtained at 300, 399, and 613 K. Quantum chemical (ab initio) calculations of the SiC 2H 4 reaction system at the G3 level support the initial formation of silirene, which rapidly isomerizes to ethynylsilane as the major pathway. Reversible formation of vinylsilylene is also an important process. The calculations also indicate the involvement of several other intermediates, not previously suggested in the mechanism. RRKM calculations are in semiquantitative agreement with the pressure dependences and isotope effects suggested by the ab initio calculations, but residual discrepancies suggest the possible involvement of the minor reaction channel, SiH 2 + C 2H 2 --> Si( (3)P 1) + C 2H 4. The results are compared and contrasted with previous studies of this reaction system.
通过激光闪光光解苯基硅烷 - d₃ 生成二氘代硅烯（SiD₂），对其与 C₂H₂ 的双分子反应进行了时间分辨动力学研究，以获得反应速率常数。该反应在气相中，于 SF₆ 浴气压力范围 1 - 100 Torr 下，在 297 - 600 K 的五个温度下进行研究。通过外推至各温度下的高压极限得到的二级速率常数符合阿伦尼乌斯方程 log( k (∞)/cm³ molecule⁻¹ s⁻¹ ) = (-10.05 ± 0.05) + (3.43 ± 0.36 kJ mol⁻¹)/ RT ln 10。通过与早期获得的 SiH₂ 与 C₂H₂ 和 C₂D₂ 反应的速率常数进行比较，利用这些速率常数获得了一套全面的同位素效应。此外，在 300、399 和 613 K 下，获得了在 He（1 - 100 Torr）存在下 SiH₂ 与 C₂H₂ 反应的压力依赖速率常数。在 G3 水平对 SiC₂H₄ 反应体系进行的量子化学（从头算）计算支持硅杂环丙烯的初始形成，其迅速异构化为乙炔基硅烷作为主要途径。乙烯基硅烯的可逆形成也是一个重要过程。计算还表明涉及其他几种中间体，这在之前的反应机理中未被提出。RRKM 计算与从头算计算所表明的压力依赖性和同位素效应在半定量上一致，但残留差异表明可能涉及次要反应通道 SiH₂ + C₂H₂ --> Si(³P₁) + C₂H₄。将结果与该反应体系的先前研究进行了比较和对比。
