On enantiomeric excesses obtained from racemic mixtures by using circularly polarized pulsed lasers of varying durations Original Research Article

The control of the populations of the left- versus the right-handed excited molecular states, arising from the interaction of a circularly polarized pulsed laser with the ground states of the enantiomers of a chiral molecule, is discussed using the pulse duration as a control variable for a fixed laser intensity. While the relative population of the excited enantiomeric states can, in principle, be controlled totally for absorbing molecules having a fixed orientation with respect to the laser beam, the control of the relative population is much reduced for randomly orientated samples of absorbing molecules. An approach for optimizing the difference in the relative populations of the enantiomers for the random situation is discussed and differences of up to ∼6% are obtained for a model two-level chiral molecule within the rotating wave approximation. The implications regarding the separation of enantiomers in a racemic mixture, and in the determination of enantiomeric excesses, are discussed.