Laser-induced molecular rotational dynamics: A high-frequency Floquet approach - art. no. 023409

The rotational dynamics of a molecule interacting with a linearly polarized intense laser held is investigated. A high-frequency Floquet approach proc eeding to an adiabatic separation between "fast" field-oscillation modes an d "slow" molecular rotational motion is adopted, which leads to an approxim ate effective Hamiltonian. A thorough analysis of the validity of the appro ximation is provided by examining the neglected terms. The HCN molecule, wi thin a linear rigid-rotor description, is taken as an illustration of the m odel. The anisotropic interaction of the electric-field vector of the inten se laser radiation with the permanent dipole moment and the polarizability of the molecule creates aligned pendular states. These states are eigenfunc tions of an effective Hamiltonian governed by a cos(2)theta potential (with theta the angle between the molecular axis and the field vector) and serve as a basis for the interpretation and prediction of alignment dynamics. Th e results show, in particular, the difference in the alignment properties o f linear HCN when excited by sudden versus adiabatic laser pulses, where ad iabatic transport from field-fret to pendular states can be evoked.