Larsen R Wugt, Zielke Philipp, Suhm Martin A
Institut für Physikalische Chemie, Universität Göttingen, Tammannstrasse 6, D-37077 Göttingen, Germany.
J Chem Phys. 2007 May 21;126(19):194307. doi: 10.1063/1.2732745.
A comprehensive study of the OH and OD stretching fundamentals in clusters of methanol and its isotopomers CH(3)OD, CD(3)OH, and CD(3)OD provides detailed insights into the hydrogen-bond mediated coupling as a function of cluster size. The combination of infrared and Raman supersonic jet spectroscopy enables the observation and assignment of all hydrogen-bonded OH stretching modes of isolated methanol trimer and methanol tetramer. A consistent explanation for the spectral complexity observed more than a decade ago in methanol trimer in terms of low-frequency methyl umbrella motions is provided. Previous explanations based on cluster isomerism or anharmonic resonances are ruled out by dedicated jet experiments. The first experimental lower bound for concerted quadruple proton transfer in S(4) symmetric methanol tetramer is derived and compared with theoretical predictions. The observed isotope effects offer insights into the anharmonicity of the localized OH bond. The performance of harmonic B3LYP and MP2 calculations in predicting hydrogen-bond-induced spectral shifts and couplings is investigated.
对甲醇及其同位素异构体CH(3)OD、CD(3)OH和CD(3)OD团簇中OH和OD伸缩基频进行的全面研究，深入揭示了氢键介导的耦合作用与团簇大小的关系。红外和拉曼超音速喷射光谱相结合，能够对孤立的甲醇三聚体和甲醇四聚体中所有氢键OH伸缩模式进行观测和归属。针对十多年前在甲醇三聚体中观察到的光谱复杂性，给出了基于低频甲基伞状运动的一致解释。专门的喷射实验排除了先前基于团簇异构或非谐共振的解释。推导了S(4)对称甲醇四聚体中协同四重质子转移的首个实验下限，并与理论预测进行了比较。观察到的同位素效应为局域OH键的非谐性提供了见解。研究了谐波B3LYP和MP2计算在预测氢键诱导的光谱位移和耦合方面的性能。
