Effective Hamiltonian for femtosecond vibrational dynamics

Time propagation of zero-order states of an effective spectroscopic Hamiltonian is tested against femtosecond time dependent dynamics of adiabatic wavepackets evolving on a model potential energy surface for two coupled modes of the radical HO(2) with multiple potential wells and above barrier motion. A generalized Hamiltonian which breaks the usual conserved polyad action by including extra resonance couplings (V(2:1) and V(3:1)) successfully describes the time evolution after the further addition of two ultrafast couplings. These new couplings are a nonresonant coupling a(1)a(2) + a(1)(dagger)a(2)(dagger) and a resonant coupling V(1:1) that functions as an ultrafast term because the system is far from 1: 1 frequency resonance. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3650481]