Selective preparation of enantiomers by laser pulses: From optimal controlto specific pump and dump transitions

Starting from optimal control, various series of infrared, ultrashort laser pulses with analytical shapes are designed in order to drive a preoriented molecule from its ground torsional state, which represents the coherent su perposition of left and right atropisomers, towards a single enantiomer. Cl ose analysis of the population dynamics, together with the underlying symme try selection rules for the laser induced transitions, yields the mechanism . Namely, the molecule is driven from its ground vibrational state towards the coherent superposition of the lowest doublet of states via a doublet of excited torsional states with opposite symmetries. This pump-and-dump mech anism can be achieved by simpler series of analytical laser pulses. This de composition of the optimal pulse into analytical subpulses allows us to des ign different scenarios for the selective preparation of left or right enan tiomers. Exemplary this is demonstrated by quantum simulations of represent ative wave packets for the torsional motions of the model system, H2POSH, i n the electronic ground state, based on the ab initio potential energy surf ace, and with ab initio dipole couplings. (C) 2000 American Institute of Ph ysics. [S0021-9606(00)00940-5].