Milischuk Anatoli A, Ladanyi Branka M
Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523-1872, USA.
J Chem Phys. 2014 Nov 14;141(18):18C513. doi: 10.1063/1.4896218.
We report the results of a molecular simulation study of polarizability anisotropy relaxation for water confined in approximately cylindrical silica pores, with diameters in the range from 20 to 40 Å. In our calculations, we use a polarizability model that includes molecular and interaction-induced components. In agreement with optical Kerr effect experimental data, we find strong confinement effects on the relaxation rate of water polarizability anisotropy. Given that water molecular polarizability anisotropy is small, much of the intensity of the polarizability anisotropy response comes from the interaction-induced component. However, we find that, at longer times, the relaxation properties of this component strongly resemble those of collective reorientation, the mechanism by which the molecular polarizability anisotropy relaxes. We also find that the relevant collective orientational relaxation differs considerably from single molecule reorientation and that this difference varies with the extent of confinement. Our investigation of the effects of axial-radial pore anisotropy indicates that these effects play a minor role in water polarizability anisotropy relaxation in this pore diameter range.
我们报告了一项分子模拟研究的结果，该研究针对限制在直径范围为20至40埃的近似圆柱形二氧化硅孔隙中的水的极化率各向异性弛豫。在我们的计算中，我们使用了一个包含分子和相互作用诱导成分的极化率模型。与光学克尔效应实验数据一致，我们发现水的极化率各向异性弛豫速率受到强烈的限制效应。鉴于水分子极化率各向异性较小，极化率各向异性响应的大部分强度来自相互作用诱导成分。然而，我们发现，在较长时间内，该成分的弛豫特性与分子极化率各向异性弛豫的集体重排机制非常相似。我们还发现，相关的集体取向弛豫与单分子重排有很大不同，并且这种差异随限制程度而变化。我们对轴向-径向孔隙各向异性影响的研究表明，在这个孔径范围内，这些影响在水的极化率各向异性弛豫中起次要作用。
