亚乙基硫脲分子键伸缩模式与全耦合模式键极化率的对比及其拉曼激发虚态的相关研究

The comparison of temporal bond polarizabilities of the nonresonant Raman excited virtual state of ethylene thiourea by two different algorithms

从拉曼峰强着手,得到了键伸缩模式与全耦合模式两种不同计算条件下,亚乙基硫脲(ethylene thiourea,ETU)分子的键极化率,并比较分析了两种计算结果的异同.研究表明:在键伸缩模式的算法中,仅考虑势能分布中键对称伸缩比重相对较大的部分拉曼峰参与极化率计算,显然忽略了键伸缩与键弯曲间的相互耦合,造成了与弯曲振动耦合较强的部分键伸缩极化率值存在一定误差.因此,此方法虽能使问题简化,但却丢失了一些信息.而全耦合模式算法考虑了所有振动模式(键伸缩与键弯曲)相互影响的情况,能更全面的反映键电荷的分布情况,但却会使问题的求解过程变得复杂.同时,在拉曼激发虚态的相关研究中,两种计算方法却得到几乎一致的键极化率弛豫方式(呈单指数规律衰减)及相同的衰减特征时间.

We studied the temporal bond polarizabilities of ethylene thiourea （ETU） from the Raman intensities by two different algorithms. One algorithm includes only the bond stretching modes and the other includes all bond modes. Our analysis shows that,the algorithm using bond stretching modes,in which only the part of Raman peaks whose vibrational modes have relatively larger proportion in the bond stretching are considered,may have larger errors in certain situations where the stretching and bending modes have significant coupling. Otherwise,this algorithm is just suitable,although it may lose certain physical information. The bond polarizabilities provide much information concerning the electronic distribution of nonresonant Raman excited virtual state. At the initial moment of the 514. 5 nm excitation,the tendency of the excited electrons is to spread to the molecular periphery. Meanwhile,the relaxation process of the bond polarizability and the characteristic times for these two models are almost the same.