Vibration-torsion interaction in the microwave spectrum of internally hydrogen-bonded methylmalonaldehyde
Vibration-torsion interaction in the microwave spectrum of internally hydrogen-bonded methylmalonaldehyde
复制标题
内部氢键甲基丙二醛微波谱中的振动-扭转相互作用
DOI：
10.1016/0022-2852(81)90103-x
复制
发表时间：
1981
期刊：
影响因子：
--
通讯作者：
N. Sanders
中科院分区：
文献类型：
--
作者：
N. Sanders
甲基丙二醛的微波光谱已被测量和分子显示在分子内氢键（螯合环）的形式在气相中。该光谱显示了两种大振幅内部运动的影响：甲基绕其对称轴的扭转和氢键氢穿过势垒到等效位置的隧道（结合适当的CH 3旋转）。这两种运动通过扭转坐标中三重对称的扭转反演势能项耦合。一个两个振动加旋转模型的发展和应用，以解释相当大的扰动的纯旋转过渡从一个刚性转子图案在四个基态子级。在非简并能级上观察到的扭转反转分裂（O <$CH <$C（CH 3）<$CHOH为2.8004 cm− 1，O <$CH <$C（CH 3）<$CHOD为0.35920 cm− 1，O <$CH <$C（CD 3）<$CHOH为0.92590 cm− 1）已经被很好地确定，并且正如预期的那样，强烈地依赖于适当的同位素取代。实验导出的参数进行了讨论的有效反转扭转势面。的数据是不同意的范围内的势垒值确定从头算全几何优化和约束C 2 v几何优化的分子轨道计算的比较。由于预期的同位素依赖性的有效表面和大量的参数，目前还不清楚是否更准确的拟合数据是合理的。
The microwave spectrum of methylmalonaldehyde has been measured and the molecule shown to be in an intramolecularly hydrogen-bonded (chelate ring) form in the gas phase. The spectrum shows the effects of two large amplitude internal motions: the torsion of the methyl group about its symmetry axis and the tunneling of the hydrogen-bond hydrogen through a potential barrier to an equivalent position (combined with an appropriate CH 3 rotation). The two motions are coupled through the torsion-inversion potential energy term of threefold symmetry in the torsional coordinate. A two vibration-plus-rotation model is developed and applied to explain the sizeable perturbations of the pure rotational transitions from a rigid rotor pattern in four ground-state sublevels. The observed torsion-inversion splittings in the nondegenerate level (2.8004 cm− 1 for O CH C (CH 3) CHOH, 0.35920 cm− 1 for O CH C (CH 3) CHOD and 0.92590 cm− 1 for O CH C (CD 3) CHOH) are quite well determined and, as expected, depend strongly upon appropriate isotopic substitutions. The experimentally derived parameters are discussed in terms of an effective inversion-torsion potential surface. The data are not in disagreement with a range of barrier values determined from comparison of ab initio full geometry-optimized and constrained C 2v geometry-optimized molecular orbital calculations. Because of the expected isotope dependence of the effective surface and the large number of parameters involved, it is not clear whether more accurate fitting to the data is justified.