Vibrations Stark effects, which are the effects of electric fields on vibrational spectra, were measured for the C-N stretch mode of several small nitriles. Samples included unconjugated and conjugated nitriles, and mono- and dinitriles. They were immobilized in frozen 2-methyl-tetrahydrofuran glass and analyzed in externally applied electric fields using an FTIR; details of the methodology are presented. Difference dipole moments, Δμ, equivalent to the linear Stark tuning rate, range from 0.01/f to 0.04/f Debye (0.2/f to 0.7/f cm~(-1)/(MV/cm)) for most samples, with aromatic compounds toward the high end and symmetric dinitriles toward the low end (the local field correction factor, f, is expected to be similar for all these samples). Most quadratic Stark effects are small and negative, while transition polarizabilities are positive and have a significant effect on Stark line shapes. For aromatic nitriles, transition dipoles and Δμ values corelate with Hammett numbers. Symmetric dinitrile Δμ values decrease monotonically with increasing conjugation of the connecting bridge, likely due to improved mechanical coupling and, to a lesser extent, and increased population of inversion symmetric conformations. Δμ values are close to those expected from bond anharmonicity and ab initio predictions.
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机译：振动对于几个小腈的C-N拉伸模式，测量了电场对振动谱的斯塔克效应。样品包括未结合的和结合的腈，以及单腈和二腈。将它们固定在冷冻的2-甲基-四氢呋喃玻璃中，并使用FTIR在外部施加的电场中进行分析;介绍了该方法的详细信息。大多数样品的偶极矩差Δμ等于线性Stark调谐速率，范围为0.01 / f至0.04 / f Debye（0.2 / f至0.7 / f cm〜（-1）/（MV / cm）），其中芳族化合物朝向高端，而对称二腈则朝向低端（所有这些样品的局部场校正因子f预计都相似）。大多数二次斯塔克效应较小且为负，而过渡极化率为正，并且对斯塔克线形有显着影响。对于芳族腈，跃迁偶极子和Δμ值与哈米特数相关。对称二腈Δμ值随着连接桥的共轭增加而单调降低，这可能是由于机械耦合改善以及反对称对称构象的增加（在较小程度上）。 Δμ值接近于键非谐性和从头算的预期值。
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