ON ENANTIOMERIC EXCESSES OBTAINED FROM RACEMIC MIXTURES BY USING CIRCULARLY-POLARIZED PULSED LASERS OF VARYING DURATIONS

The control of the populations of the left-versus the right-handed exc ited molecular states, arising from the interaction of a circularly po larized pulsed laser with the ground states of the enantiomers of a ch iral molecule, is discussed using the pulse duration as a control vari able 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 fo r randomly orientated samples of absorbing molecules. An approach for optimizing the difference in the relative populations of the enantiome rs for the random situation is discussed and differences of up to simi lar to 6% are obtained for a model two-level chiral molecule within th e rotating wave approximation. The implications regarding the separati on of enantiomers in a racemic mixture, and in the determination of en antiomeric excesses, are discussed. (C) 1998 Elsevier Science B.V.