Theory of Selective Preparation of Enantiomers by Laser Pulses
Theory of Selective Preparation of Enantiomers by Laser Pulses
复制标题
激光脉冲选择性制备对映体的理论
DOI：
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发表时间：
2003
期刊：
影响因子：
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通讯作者：
D. Kröner
中科院分区：
文献类型：
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作者：
D. Kröner
手头的工作涉及从外消旋体开始的激光脉冲控制制备纯对映体的模拟。模拟基于H2POSH和（4-甲基-环己基）氟甲烷模型体系的一维和二维从头算势和偶极子函数。两种分子都具有手性轴，但它们在外消旋化方面的稳定性不同。沿着手性轴的异构化，由对称从头算双最小势描述，允许一种对映体转化为另一种对映体。量子动力学计算的初始状态是由预取向分子在低温下的外消旋混合物定义的。开发了几种控制机制，允许对外消旋体中的对映体进行区分，并通过分析超短激光脉冲选择性地增强一种对映体的种群。为了控制系统的手性，使用了激光耦合到两个不同对称的偶极子分量，即一个偶极子分量相对于从一个对映体到另一个对映体的转化路径的反转中心需要进行变换，另一个偶极子分量需要进行变换。此外，需要在电子基态或电子激发态中存在一个具有梯度对称或非梯度对称的中间量子态。激光脉冲的对映体选择性受其偏振方向的显著控制，而分子相对于偏振方向的取向对激光控制的效率起着重要的作用。
The work at hand deals with the simulation of the laser pulse-controlled preparation of pure enantiomers starting from a racemate. The simulations are based on oneand two-dimensional ab initio potentials and dipole functions of the model systems H2POSH and (4-methyl-cyclohexylidene)fluoromethane. Both molecules possess a chiral axis, but they differ in stability with respect to racemization. The isomerization along the chiral axis, described by a symmetric ab initio double minimum potential, allows the conversion of one enantiomer into the other. The initial state of the quantum dynamical calculations is defined by a racemic mixture of pre-oriented molecules at low temperature. Several control mechanisms were developed which allow the discrimination of the enantiomers in the racemate and the selective enhancement of the population of one enantiomer over the other by means of analytical utrashort laser pulses. To control the chirality of the system, laser coupling to two dipole components of different symmetry are used, i.e. one of the dipole components needs to be gerade and the other ungerade with respect to the center of inversion of the conversion path from one enantiomer to the other. In addition, an intermediate quantum state in the electronic ground or electronic excited state with either gerade or ungerade symmetry is required. The enantio-selectivity of the laser pulses is significantly controlled by their polarization direction, whereas the orientation of the molecules with respect to the polarization direction plays an important role for the efficiency of the laser control.