CLASSICAL AND QUANTUM CHAOS IN MOLECULAR ROTATIONAL-EXCITATION BY AC ELECTRIC-FIELDS

The interaction of diatomic molecules with an ac electric field is des cribed by a periodically driven rigid rotor model Hamiltonian. Numeric al studies of the classical and quantum dynamics reveal a remarkably c lose correspondence between classically chaotic dynamics and quantum t ime evolution. Unlike the periodically kicked rotor all the quasienerg y states located in the (bounded) chaotic region in phase space are ex tended states. Expanded in the free rotor basis, their coefficients fu llfill the statistical predictions for random vectors. Consequently, e ven in off resonance condition the probability for transfering angular momentum to the diatomic molecule is large and eventually the first j (m) excited rotational states will be ''democratically'' populated. Th e value of j(m) is determined by the bounded chaotic region in phase s pace. The rotational occupation probability shows an erratic behavior with fluctuations following the statistical predictions for random qua ntum states.