Overtone State‐Selective Isomerization by a Series of Picosecond Infrared Laser Pulses: Model Simulations for Be2H3D‐(C2v) → C3v)

Abstract

AbstractThe vibrational state‐selective isomerization of Be2H3D− in the electronic ground state by a series of picosecond infrared laser pulses is simulated, using a one‐dimensional model in the framework of the Born‐Oppenheimer and semiclassical dipole approximations. Three pulses pumping the sequential overtone transitions serve to excite the anion from its vibrational ground state, representing the stable C2v configuration, to a delocalized vibrational state with energy close to the potential energy barrier. These three pump‐pulses are followed by a dump‐pulse which induces the overtone transition from the delocalized state to a vibrationally‐excited state of the slightly less stable isomer of Be2H3D− with C2v symmetry. The overall reaction probability for optimal laser pulses with sin2‐shapes is about 95%.The model is based on ab initio calculations of the potential energy surface and the dipole function for the electronic ground state of Be2H3D− at the MP4/6–31 ++G* level, with corresponding vibrational energies and dipole transition matrix elements. The laser‐stimulated dynamics of the ultrafast state‐selective isomerization is described by a representative, time‐dependent wave packet which is driven by the laser pulses, according to the time‐dependent Schrödinger equation, equivalent to a set of linear differential equations for the time‐dependent amplitudes of vibrational eigenstates which constitute the wave packet. This set ofdifferential equations is solved by using both standard numerical techniques and an efficient quasiresonant smoothing algorithm.