Department of Physics and Astronomy, University of Nevada, Las Vegas, Nevada 89154-4002, USA.
J Chem Phys. 2018 Apr 7;148(13):134504. doi: 10.1063/1.5012901.
Polarization and angle dependence of hyper-Rayleigh scattering (HRS) measured for liquid acetonitrile and dimethyl sulfoxide (DMSO) is analyzed in terms of contributions from randomly oriented molecules and additional contributions produced during intermolecular collisions and induced by the electric field of dissolved ions. All three contributions show the effect of long-range correlation, and the correlation functions are determined using the HRS observations combined with the results of molecular dynamics simulations. HRS from acetonitrile is polarized transverse to the scattering vector. This is due to long-range molecular orientation correlation produced by the dipole-dipole interaction, and correlation at distances r > 100 nm must be included to account for the HRS observations. Analysis of the HRS measurements for acetonitrile determines the length scale a = 0.185 nm for the long-range longitudinal and transverse orientation correlation functions B=-2B=a/r. Transverse polarized collision-induced HRS is also observed for acetonitrile, indicating long-range correlation of intermolecular modes. Strong longitudinal HRS is induced by the radial electric field of dissolved ions in acetonitrile. For DMSO, the angle between the molecular dipole and the vector part of the first hyperpolarizability tensor is about 100°. As a result, HRS from the randomly oriented molecules in DMSO is nearly unaffected by dipole correlation, and ion-induced HRS is weak. The strong longitudinal polarized HRS observed for DMSO is due to the collision-induced contribution, indicating long-range correlation of intermolecular modes. The HRS observations require correlation that has r long-range asymptotic form, for molecular orientation and for intermolecular vibration and libration, for both acetonitrile and DMSO.
液体乙腈和二甲基亚砜（DMSO）的超瑞利散射（HRS）的偏振和角度依赖性，从随机取向分子的贡献以及分子间碰撞产生的额外贡献和溶解离子的电场诱导进行分析。所有这三个贡献都显示了长程相关的效应，相关函数是使用 HRS 观察结果与分子动力学模拟的结果相结合来确定的。乙腈的 HRS 是横向偏振的。这是由于偶极-偶极相互作用产生的长程分子取向相关，必须包括距离 r>100nm 的相关才能解释 HRS 观察结果。对乙腈的 HRS 测量的分析确定了长程纵向和横向取向相关函数的长度尺度 a=0.185nm，B=-2B=a/r。乙腈也观察到了横向偏振的碰撞诱导 HRS，表明了分子间模式的长程相关。乙腈中溶解离子的径向电场诱导了强烈的纵向 HRS。对于 DMSO，分子偶极矩和第一超极化率张量的矢量部分之间的角度约为 100°。结果，DMSO 中随机取向分子的 HRS 几乎不受偶极相关的影响，离子诱导的 HRS 较弱。DMSO 中观察到的强烈纵向偏振 HRS 是由于碰撞诱导的贡献，表明分子间模式的长程相关。对于乙腈和 DMSO，HRS 观察结果都需要分子取向、分子间振动和振动的长程渐近形式的相关。
