Vibrational 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 infrozen 2-methyl-tetrahydrofuran glass and analyzed in externally applied electric fields using an FTIR; details of the methodology are preseazed. Difference dipole moments. &p, equivalent to the linear Stark tuning rate, range from 0.01/f to 0.04ff Debyc (0.2/f to 0.7/f Ciii)) for most samples, with aromatic compounds toward the high end and symmetric dinitriles low end (the local field correction factor, f, is expected to be similar for all these samples). Most - effects are small and negative, while transition polarizabilities are positive and have a significantai Stark line shapes. For aromatic nitriles, transition dipoles and Ap values correlate willi Hammetr Symmetric dinitrile Ap values decrease monotonically with increasing conjugation of the connecting-e, likely due to improved mechanical coupling and, to a lesser extent, an increased population of inversion etric conformations. Ap values are close to those expected from bond anharmonicity and ab initio predictions.
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