ROTATIONAL-EXCITATION AND MOLECULAR ALIGNMENT IN INTENSE LASER FIELDS

Rotational excitation and spatial alignment in moderate intensity radi ation fields are studied numerically and analytically, using time-depe ndent quantum mechanics. Substantial rotational excitation is found un der conditions typically used in time-resolved spectroscopy experiment s. The broad rotational wave packet excited by the laser pulse is well defined in the conjugate angle space, peaking along the field polariz ation direction. Both the rotational excitation and the consequent spa tial alignment can be controlled by the choice of field parameters. Fr agment angular distributions following weak field photodissociation of the rotational wave packet are computed as a probe of the degree of a lignment. In the limit of rapid photodissociation the angular distribu tion is peaked in the forward direction, reflecting the anisotropy of the aligned state. Potential applications of the effect demonstrated r ange from reaction dynamics of aligned molecules and laser-control to material deposition and laser-assisted isotope separation. (C) 1995 Am erican Institute of Physics.