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首页> 外文期刊>The Journal of Chemical Physics >State-specific vibrational anharmonicities in cyclobutadiene and evidence for fast automerization by (C4H4)-C-12
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State-specific vibrational anharmonicities in cyclobutadiene and evidence for fast automerization by (C4H4)-C-12

机译：环丁二烯中特定于状态的振动非谐性以及（C4H4）-C-12快速自动异构化的证据

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MO computations of vibrational spectra for 1,3-cyclobutadiene (CB) and CB:CO2 van der Waals molecule isotopomers at the MP2/6-311++G(2d,2p) level of MO theory are analyzed together with the extensive Ar/CB matrix-isolation spectra of the Michl group, the low 3.2 kcal/mol (ZPE-corrected) MO-computed energy of the square-planar saddle-point for CB reported by Nakamura et al., and opportune one-dimensional analysis of the automerization energy levels of (C4H4)-C-12. The composite interpretation results in the assignment of the strongly anharmonic Raman transitions of Ar/CB observed at 723 and 1678 cm(-1) to the E-2-E-0 and E-4-E-0 transitions, respectively, in the automerization coordinate. The C-13 and D isotope dependencies of the nominal C=C stretching and delta CH wagging vibrational normal modes of the CB valence isomers depend markedly on whether the labeled HC=CH moieties of CB are mass equivalent or not, and the pronounced normal mode differences are viewed as providing different gateways into the global anharmonic PES domains. The automerization coordinate Q(a) originates as the nominal C=C stretching normal coordinate of a,, symmetry, followed by a curving to more efficiently interchange the C=C and C-C bond lengths as the square-planar D-4h configuration is approached. The latter is crossed at a geometry dilated with respect to the saddle-point, thereby providing a barrier configuration about 5 kcal/mol above the PES minima (i.e., a dilation energy of about 2 kcal/mol plus the 3.2 kcal/mol saddle-point energy). The computed zero-point levels of (C4H4)-C-12 (1-D modeling) are separated by E-1-E-0=11 cm(-1) to suggest ZP tunneling rates reaching the picosecond time scale. The analysis exposes new aspects of the intramolecular dynamics of CB, and the proposed automerization mechanism accounts for all of the presently known information pertaining to this interesting Property of the cyclobutadiene molecule. (C) 1998 American Institute of Physics. [S0021-9606(98)03148-1]. [References: 28]
机译：分析了MO理论的MP2 / 6-311 ++ G（2d，2p）水平下1,3-环丁二烯（CB）和CB：CO2 van der Waals分子异构体的振动光谱的MO计算以及广泛的Ar / Nakamura等人报道了Cich的CB基质分离光谱，CB的方平面鞍点的低3.2 kcal / mol（经ZPE校正）MO计算的能量，以及适当的一维分析（C4H4）-C-12的自旋能级复合解释导致在723和1678 cm（-1）观察到的Ar / CB强非谐拉曼跃迁分别对应于E-2-E-0和E-4-E-0跃迁。自动化坐标。 CB价态异构体的标称C = C拉伸和δCH摆动振动正态模态的C-13和D同位素依赖性显着取决于CB的标记HC = CH部分是否为质量当量以及显着的正态模态差异被视为为全球非谐PES域提供了不同的网关。自旋坐标Q（a）源自对称的a的标称C = C拉伸正态坐标，然后随着接近方形D-4h构型而弯曲以更有效地互换C = C和CC键长。后者以相对于鞍点扩张的几何形状交叉，从而在PES最小值之上提供约5 kcal / mol的势垒构型（即，约2 kcal / mol的扩张能量加上3.2 kcal / mol的鞍形-点能量）。 （C4H4）-C-12（1-D建模）的计算出的零点水平由E-1-E-0 = 11 cm（-1）分开，以表明ZP隧穿速率达到皮秒的时间尺度。该分析揭示了CB分子内动力学的新方面，并且提出的自动化机理解释了与环丁二烯分子这一有趣特性有关的所有目前已知信息。 （C）1998美国物理研究所。 [S0021-9606（98）03148-1]。 [参考：28]

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