quantum dynamics, ab initio calculations, laser pulse control, chirality
540 Chemie und zugeordnete Wissenschaften
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 one- and 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.
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