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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Ab initio chemical kinetics for SiH_2 + Si_2H _6 and SiH_3 + Si_2H_5 Reactions and the related unimolecular decomposition of Si_3H_8 under a-Si/H CVD conditions
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Ab initio chemical kinetics for SiH_2 + Si_2H _6 and SiH_3 + Si_2H_5 Reactions and the related unimolecular decomposition of Si_3H_8 under a-Si/H CVD conditions

机译：在a-Si / H CVD条件下SiH_2 + Si_2H _6和SiH_3 + Si_2H_5反应的从头算化学动力学以及Si_3H_8的相关单分子分解

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The kinetics and mechanisms for SiH_2 + Si_2H _6 and SiH_3 + Si_2H_5 reactions and the related unimolecular decomposition of Si_3H_8 have been investigated by ab initio molecular orbital theory based on the QCISD(T)/CBS//QCISD/6-311++G(d,p) method in conjunction with quantum statistical variational Rice-Ramsperger-Kassel-Marcus (RRKM) calculations. For the barrierless radical association processes, their variational transition states have been characterized by the CASPT2//CASSCF method. The species involved in the study are known to coexist under CVD conditions. The results show that the association reaction of SiH_2 and Si_2H_6 producing Si_3H_8 occurs by insertion via its lowest-energy path forming a loose hydrogen-bonding molecular complex with 8.3 kcal/mol binding energy; the reaction is exothermic by 55.0 kcal/mol. The chemically activated Si_3H_8 adduct can fragment by several paths, producing SiH_4 + SiH_3SiH (-0.7 kcal/mol), Si(SiH _3)_2 + H_2 (-1.4 kcal/mol), and SiH _3SiH_2SiH + H_2 (-1.4 kcal/mol). The predicted enthalpy changes as given agree well with available thermochemical data. Three other decomposition channels of Si3H8 occurring by Si-H or Si-Si breaking were found to be highly endothermic, and the reactions take place without a well-defined barrier. The heats of formation of Si _3H_8, SiH_2SiH, Si_2H_4, i-Si_3H_7, n-Si_3H_7, Si(SiH _3)_2, and SiH_3SiH_2SiH have been predicted and found to be in close agreement with those available data in the literature. The product branching rate constants for SiH_2 + Si _2H_6 and SiH_3 + Si_2H_5 reactions and the thermal unimolecular decomposition of Si3H 8 for all low-energy paths have been calculated with multichannel variational RRKM theory covering varying P,T conditions typically employed in PECVD and Cat-CVD processes for hydrogenated amorphous silicon (a-Si/H) film growth. The results were also found to be in good agreement with available kinetic data. Our kinetic results may be employed to model and control very large-area a-Si/H film growth for a new generation of solar cell applications.
机译：基于QCISD（T）/ CBS // QCISD / 6-311 ++ G的从头算分子轨道理论，研究了SiH_2 + Si_2H _6和SiH_3 + Si_2H_5反应以及Si_3H_8相关的单分子分解的动力学和机理。 d，p）方法结合量子统计变分莱斯-拉姆斯伯格-卡塞尔-马库斯（RRKM）计算。对于无障碍自由基缔合过程，已经通过CASPT2 // CASSCF方法表征了它们的变迁过渡态。已知该研究涉及的物种在CVD条件下共存。结果表明，产生SiH_2和Si_2H_6的Si_3H_8的缔合反应是通过其最低能量路径插入而形成的，形成具有8.3 kcal / mol结合能的疏松的氢键分子复合物。反应放热为55.0 kcal / mol。化学活化的Si_3H_8加合物可以通过多种途径裂解，从而生成SiH_4 + SiH_3SiH（-0.7 kcal / mol），Si（SiH _3）_2 + H_2（-1.4 kcal / mol）和SiH _3SiH_2SiH + H_2（-1.4 kcal / mol） ）。给出的预计焓变与可利用的热化学数据非常吻合。发现通过Si-H或Si-Si断裂而发生的Si3H8的其他三个分解通道是高度吸热的，并且反应在没有明确定义的障碍的情况下进行。预测了Si _3H_8，SiH_2SiH，Si_2H_4，i-Si_3H_7，n-Si_3H_7，Si（SiH _3）_2和SiH_3SiH_2SiH的形成热，并与文献中的可用数据非常一致。 SiH_2 + Si _2H_6和SiH_3 + Si_2H_5反应的产物支化速率常数以及所有低能路径下Si3H 8的热单分子分解均采用多通道变分RRKM理论计算得出，该理论涵盖了PECVD和Cat-氢化非晶硅（a-Si / H）膜生长的CVD工艺。还发现结果与可获得的动力学数据高度吻合。我们的动力学结果可用于为新一代太阳能电池应用建模和控制非常大面积的a-Si / H膜生长。

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