la Cour Jansen Thomas, Knoester Jasper
Institute for Theoretical Physics and Materials Science Centre, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
J Chem Phys. 2006 Jan 28;124(4):044502. doi: 10.1063/1.2148409.
A method for modeling infrared solvent shifts using the electrostatic field generated by the solvent is presented. The method is applied to the amide I vibration of N-methyl acetamide. Using ab initio calculations the fundamental frequency, anharmonicity, and the transition dipoles between the three lowest vibrational states are parametrized in terms of the electrostatic field. The generated map, which takes into account the electric field and its gradients at four molecular positions, is tested in a number of common solvents. Agreement of solvent shift and linewidths with experimental Fourier transform infrared (FTIR) data is found to within seven and four wave numbers, respectively, for polar solvents. This shows that in these solvents electrostatic contributions dominate solvation effects and the map is transferable between these types of solvents. The effect of motional narrowing arising from the fast solvent fluctuations is found to be substantial for the FTIR spectra. Also the two-dimensional infrared (2DIR) spectra, simulated using the constructed map, reproduce experimental results very well. The effect of anharmonicity fluctuations on the 2DIR spectra was found to be negligible.
提出了一种利用溶剂产生的静电场对红外溶剂位移进行建模的方法。该方法应用于N-甲基乙酰胺的酰胺I振动。使用从头算计算，根据静电场对三个最低振动状态之间的基频、非谐性和跃迁偶极矩进行参数化。考虑了四个分子位置处的电场及其梯度的生成图谱，在多种常见溶剂中进行了测试。对于极性溶剂，发现溶剂位移和线宽与实验傅里叶变换红外（FTIR）数据的一致性分别在七个和四个波数范围内。这表明在这些溶剂中，静电贡献主导了溶剂化效应，并且该图谱在这些类型的溶剂之间是可转移的。发现快速溶剂波动引起的运动窄化效应对于FTIR光谱来说是相当大的。此外，使用构建的图谱模拟的二维红外（2DIR）光谱也能很好地重现实验结果。发现非谐性波动对2DIR光谱的影响可以忽略不计。
