Schmidt J R, Corcelli S A, Skinner J L
Theoretical Chemistry Institute and Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706, USA.
J Chem Phys. 2005 Jul 22;123(4):044513. doi: 10.1063/1.1961472.
In the context of vibrational spectroscopy in liquids, non-Condon effects refer to the dependence of the vibrational transition dipole moment of a particular molecule on the rotational and translational coordinates of all the molecules in the liquid. For strongly hydrogen-bonded systems, such as liquid water, non-Condon effects are large. That is, the bond dipole derivative of an OH stretch depends strongly on its hydrogen-bonding environment. Previous calculations of nonlinear vibrational spectroscopy in liquids have not included these non-Condon effects. We find that for water, inclusion of these effects is important for an accurate calculation of, for example, homodyned and heterodyned three-pulse echoes. Such echo experiments have been "inverted" to obtain the OH stretch frequency time-correlation function, but by necessity the Condon and other approximations are made in this inversion procedure. Our conclusion is that for water, primarily because of strong non-Condon effects, this inversion may not lead to the correct frequency time-correlation function. Nevertheless, one can still make comparison between theory and experiment by calculating the experimental echo observables themselves.
在液体振动光谱学的背景下，非康登效应是指特定分子的振动跃迁偶极矩对液体中所有分子的转动和平动坐标的依赖性。对于强氢键体系，如水，非康登效应很大。也就是说，OH伸缩振动的键偶极导数强烈依赖于其氢键环境。先前对液体非线性振动光谱的计算未包括这些非康登效应。我们发现，对于水而言，考虑这些效应对于准确计算例如零差和外差三脉冲回波非常重要。此类回波实验已被“反转”以获得OH伸缩振动频率时间相关函数，但在该反转过程中必然会进行康登及其他近似。我们的结论是，对于水，主要由于强烈的非康登效应，这种反转可能不会得到正确的频率时间相关函数。然而，通过计算实验回波可观测量本身，仍可进行理论与实验之间的比较。
