模式耦合对反常氢键系统中振动频率蓝移的影响(英文)

Effects of Mode-Mode Coupling on Vibrational Frequency Blue Shift in Improper H-Bonded Systems

反常氢键所引起的NH/CH键的键长缩短被普遍地认为必然会引起其振动频率的蓝移.本文的计算结果显示非谐性效应可能会使相应的蓝移大幅度减小.其中模式耦合起着非常重要的作用.在一些例子中,这种强的相互作用可能会导致一些基于谐振子模型计算所预言的气相中的蓝移频率实际上发生红移.尽管这些计算结果有待于通过相应体系中的气相红外(IR)光谱来进行确认,一些已报道的基质隔离红外光谱的实验结果已显示出对这些计算结果的支持.

Bond shortening of NH/CH due to improper hydrogen bonding is always thought to be accompanied by a blue shift in its corresponding frequency. However, results here show that owing to anharmonic effects, especially the contribution of mode-mode coupling, the blue shift could be greatly decreased. The strong interaction may even, in some cases, cause the previously predicted blue-shifting frequencies by harmonic methods to be red-shifted instead in the gas phase. Though these results need to be clearly verified by further infrared （IR） spectrum experiments in the gas phase for the selected systems, comparisons with previous IR results obtained from matrix isolation experiments strongly support the results of the calculations.