Theoretical study of unimolecular decomposition of allene cations
Theoretical study of unimolecular decomposition of allene cations
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DOI：
10.1063/1.3037204
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发表时间：
2008-12-14
影响因子：
4.4
通讯作者：
Bandrauk, A. D.
中科院分区：
文献类型：
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作者：
Mebel, A. M.;Bandrauk, A. D.
在密度泛函或完全活性空间自洽场水平上进行了从头耦合团簇和多参考扰动理论计算以及几何优化，以计算电离能并揭示丙二烯和丙炔阳离子C(3)H(4)(n+)(n=1-3)的解离机制。结果表明，单阳离子的主要分解通道是c-C(3)H(3)(+)+H，吸热37.9 kcal/mol，并通过43.1 kcal/mol的势垒发生，H(2)CCCH(+)+H和HCCCH(+)+H(2)可能有少量贡献。对于双阳离子，预测竞争反应通道为 c-C(3)H(3)(+)+H(+)、H(2)CCCH(+)+H(+) 和 CCCH(+)+H(3)(+)，解离能分别为 -20.5、8.5 和 3.0 kcal/mol。计算揭示了 H(3)(+) 损失的 H(2) 漫游机制，其中首先形成中性 H(2) 片段，然后漫游并从剩余分子片段中提取质子，然后离开指示。根据 Rice-Ramsperger-Kassel-Marcus 对各个反应步骤的能量依赖性速率常数的计算，相对产物产率随可用内能的变化而变化，在 70-75 kcal/mol 的能量范围内，c-C(3)H(3)(+)+H(+) 是主要产物，略高于 69.6kcal/mol 的解离阈值，CCCH(+)+H(3)(+) 在更高的能量范围内接管。能量。发现 C(3)H(4)(3+) 三阳离子不是很稳定，丙二烯和丙炔的解离阈值分别为 18.5 和 3.7 kcal/mol。 C(3)H(4)(3+)、H(2)CCCH(2)(+)+H(+)、CHCHCH(2)(+)+H(+)、C(2)H(2)(2+)+CH(2)(+)和CCH(2)(2+)+CH(2)(+)的各种库仑爆炸产物都是强放热的(98-185 kcal/mol)。 C(3)H(4) 的四正离子被认为是不稳定的，因此在分子解体之前不能从该分子中除去超过三个电子。将理论结果与丙二烯和丙炔库仑爆炸的实验观察结果进行了比较。 (C) 2008 年美国物理研究所。 [DOI：10.1063/1.3037204]
Ab initio coupled clusters and multireference perturbation theory calculations with geometry optimization at the density functional or complete active space self-consistent-field levels have been carried out to compute ionization energies and to unravel the dissociation mechanism of allene and propyne cations, C(3)H(4)(n+)(n=1-3). The results indicate that the dominant decomposition channel of the monocation is c-C(3)H(3)(+)+H, endothermic by 37.9 kcal/mol and occurring via a barrier of 43.1 kcal/mol, with possible minor contributions from H(2)CCCH(+)+H and HCCCH(+)+H(2). For the dication, the competing reaction channels are predicted to be c-C(3)H(3)(+)+H(+), H(2)CCCH(+)+H(+), and CCCH(+)+H(3)(+), with dissociation energies of -20.5, 8.5, and 3.0 kcal/mol, respectively. The calculations reveal a H(2)-roaming mechanism for the H(3)(+) loss, where a neutral H(2) fragment is formed first, then roams around and abstracts a proton from the remaining molecular fragment before leaving the dication. According to Rice-Ramsperger-Kassel-Marcus calculations of energy-dependent rate constants for individual reaction steps, relative product yields vary with the available internal energy, with c-C(3)H(3)(+)+H(+) being the major product just above the dissociation threshold of 69.6kcal/mol, in the energy range of 70-75 kcal/mol, and CCCH(+)+H(3)(+) taking over at higher energies. The C(3)H(4)(3+) trication is found to be not very stable, with dissociation thresholds of 18.5 and 3.7 kcal/mol for allene and propyne, respectively. Various products of Coulomb explosion of C(3)H(4)(3+), H(2)CCCH(2)(+)+H(+), CHCHCH(2)(+)+H(+), C(2)H(2)(2+)+CH(2)(+), and CCH(2)(2+)+CH(2)(+) are highly exothermic (by 98-185 kcal/mol). The tetracation of C(3)H(4) is concluded to be unstable and therefore no more than three electrons can be removed from this molecule before it falls apart. The theoretical results are compared to experimental observations of Coulomb explosions of allene and propyne. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.3037204]