arXiv physics/01010512001-01-10physics.chem-phphysics.comp-ph

用W2理论计算了亚甲基亚胺的生成热CH2 = NH和亚甲基铵离子的生成热CH2NH2 +

Definitive heat of formation of methylenimine, CH2=NH, and of methylenimmonium ion, CH2NH2+, by means of W2 theory

Glenisson de Oliveira, Jan M. L. Martin, Indira K. C. Silwal, Joel F. Liebman

备注：: RevTeX, 20 pages. J. Comput. Chem., in press JCC10266/F-204 (Paul von Ragué Schleyer festschrift) Supplementary material: complete CCSD(T)/cc-pVTZ quartic force field available at http://theochem.weizmann.ac.il/web/papers/ch2nh.html
发表信息：: Journal of Computational Chemistry 22, 1297-1305 (2001)

摘要：

通过W2（Weizmann-2）从头算热化学方法解决了一个长期存在的关于亚甲基亚胺生成热的争议。我们的最佳计算值，Δ Hf 298（CH 2NH）=21.1+/-0.5千卡/摩尔和Δ Hf 298（CH 2NH 2+）=179.4+/-0.5千卡/摩尔，与最近的测量结果非常一致，但不确定性要小得多。作为一个副产品，我们获得了有史以来第一次准确的亚甲基亚胺的非谐力场：考虑到适当的共振，实验气相带的起源都再现优于10 cm-1。考虑到完全非谐零点振动能和B3 LYP/cc-pVTZ谐波频率之间的差异，比例为0.985，表明即使在基准工作中，对于刚性分子，通常也可以省去非谐零点振动能的计算。

英文摘要：

A long-standing controversy concerning the heat of formation of methylenimine has been addressed by means of the W2 (Weizmann-2) ab initio thermochemical approach. Our best calculated values, DeltaHf298(CH2NH)=21.1+/-0.5 kcal/mol and DeltaHf298(CH2NH2+)=179.4+/-0.5 kcal/mol, are in good agreement with the most recent measurements but carry a much smaller uncertainty. As a by-product, we obtain the first-ever accurate anharmonic force field for methylenimine: upon consideration of the appropriate resonances, the experimental gas-phase band origins are all reproduced to better than 10 cm-1. Consideration of the difference between a fully anharmonic zero-point vibrational energy and B3LYP/cc-pVTZ harmonic frequencies scaled by 0.985 suggests that the calculation of anharmonic zero-point vibrational energies can generally be dispensed with, even in benchmark work, for rigid molecules.

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