Adiabatic representation for the dynamics of two-channel molecular systems driven by arbitrarily shaped pulses

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Abstract
The formalism developed recently by Nguyen-Dang, Manoli, and Abou-Rachid [Phys. Rev. A 43, 5012 (1991)] describes nonperturbatively the dynamics of N-level systems in the presence of a laser pulse in terms of a generalized adiabatic evolution. This formalism is adapted to multichannel molecular systems, defining a time-dependent electronic representation for the dynamics of molecular excitations induced by a short, arbitrarily shaped laser pulse. For two-channel systems, this representation is parametrized by an effective pulse area and Berry phases, which depend on nuclear coordinates. Laser-induced nonadiabatic couplings are studied analytically for a hyperbolic-secant pulse. In addition, their effects are examined in numerical studies of wave packets in simple two-channel model systems driven by a short Gaussian pulse.