Mode selective dissociation of vibrationally excitedABAmolecular resonances stimulated by a picosecond infrared laser pulse

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Abstract
Ps IR laser pulse induced dissociation of vibrationally excited ABA* molecular resonances is simulated by simple model calculations. The stretching vibrations of ABA are represented by the Rosen-Thiele-Wilson coupled Morse oscillator hamiltonian with time dependent potential V(t) describing the interaction with a gaussian laser pulse in the semiclassical dipole approximation. The Schrödinger-equation is solved by Fast-Fourier-Transform propagation. The resulting wavefunctions ψt yield mode selective effects, e.g. the decays of hyperspherical and local modes with natural life times 5·92 ps and 0·07 ps are accelerated by the laser by factors 40 and 2, respectively. The mechanisms of photodissociation are analysed in detail, including laser-induced oscillations of the potential V(t) which transform dissociative frontier lobes of the wavefunction ψt of a slowly decaying hyperspherical mode into those of a rapidly dissociating local resonance.