Selective preparation of enantiomers from a racemate by laser pulses: model simulation for oriented atropisomers with coupled rotations and torsions

We design a laser pulse which drives a racemate of oriented atropisomers at low temperature to a preferential target enantiomer. The overall laser pul se consists of a series of individual circularly polarized laser pulses whi ch induce corresponding selective transitions between coupled rotational an d torsional states. The underlying theory is derived in detail for a model system. It consists of two fragments which may carry out torsional and rota tional motions around a molecular bond which is oriented along the directio n of the laser pulses. Exemplarily, results are demonstrated for the model system H2POSH in the electronic ground state, based on a quantum chemical a b initio potential and on the components of the dipole functions describing the laser-dipole interaction. The series of laser pulses for the preparati on of the pure enantiomers for this demanding system is based on analogous results for simpler scenarios, originally starting from local control. (C) 2001 Published by Elsevier Science B.V.