Vibrational Stark effects of nitriles II. Physical origins of stark effects from experiment and perturbation models
Vibrational Stark effects of nitriles II. Physical origins of stark effects from experiment and perturbation models
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DOI：
10.1021/jp011724f
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发表时间：
2002-01-24
影响因子：
2.9
通讯作者：
Boxer, SG
中科院分区：
文献类型：
--
作者：
Andrews, SS;Boxer, SG
振动斯塔克效应，即电场对振动光谱的影响，先前针对几种小腈的C-N伸缩模式进行了测量，得到了每种物质的不同偶极矩、不同极化率和跃迁极化率[Andrews，S. S.的; Boxer，S. G. J. Phys. Chem. A 2000，104，11 853]。本文解释了所观察到的斯塔克效应的物理起源，使用两个理论模型，并在此过程中，计算几个分子参数为每个腈。用微扰理论建立的单振动模式模型可以解释大部分的斯塔克效应。因为它不能考虑模式之间的耦合，这是普遍存在的和重要的共振振动和组合模式吸收，另一种模型被开发，认为是多个振动模式和三个空间自由度。据发现，不同的偶极矩产生的机械非谐性和电子扰动的化学键的组合，其中这两个因素有大约相等的幅度为腈。跃迁极化率受样品分子的电子极化率的影响，其改变了电场中原子上的部分电荷。共振跃迁的斯塔克效应被发现是等于线性组合的基础状态的影响，这解释了实验观察。对于泛音和组合跃迁，斯塔克位移被预测为分量跃迁的位移之和。从差分偶极结果可以计算出绝对泛音强度，并得到了实验验证。总之，这些理论在很大程度上解释了观测到的振动斯塔克效应的物理起源，并可以预测各种其他系统的斯塔克效应。
Vibrational Stark effects, which are the effects of electric fields on vibrational spectra, were measured previously for the C-N stretch mode of several small nitriles, yielding difference dipole moments, difference polarizabilities, and transition polarizabilities for each species [Andrews, S. S.; Boxer, S. G. J. Phys. Chem. A 2000, 104, 11 853]. This paper explains the physical origins of the observed Stark effects using two theoretical models and, in the process, computes several molecular parameters for each nitrile. A model with a single vibrational mode, developed with perturbation theory, is found to explain most of the experimental Stark effects. Because it cannot account for coupling between modes, which is ubiquitous and important for resonant vibrations and for combination mode absorption, another model is developed which considers multiple vibrational modes and three spatial degrees of freedom. It is found that difference dipole moments arise from a combination of mechanical anharmonicity and electronic perturbations of chemical bonds, where the two factors have about equal magnitudes for nitriles. Transition polarizabilities are dominated by the effects of electronic polarizability of the sample molecule, which alters the partial charges on atoms in an electric field. Stark effects of resonant transitions are found to be equal to linear combinations of the effects for the basis states, which explains an experimental observation. For overtone and combination transitions, Stark shifts are predicted to be the sums of the shifts of the component transitions. Absolute overtone intensities can be calculated from difference dipole results, which is experimentally verified. In summary, these theories largely explain the physical origins of observed vibrational Stark effects and can predict Stark effects for a wide variety of other systems.