Sensitivity of femtosecond quantum dynamics and control with respect to non-adiabatic couplings: Model simulations for the cis-trans isomerization of the dideuterated methaniminium cation

We investigate the non-radiative decay in the photo-isomerization of the dideuterated methaniminium cation HDN+=CDH by means of quantum dynamical simulations of the laser driven torsion. For the present model, the torsional dynamics is nearly adiabatic, but this is shown to be extremely sensitive to the large non-adiabatic coupling elements close to the conical intersection as well as to the apparently small values in the other domains. Neglecting those small couplings artificially changes the nearly adiabatic dynamics into diabatic dynamics. The non-adiabatic coupling terms are calculated ab initio with a test of accuracy which is based on the strict adiabaticity of pure rotational motions. Moreover, we present a novel mechanism for the enhancement of the laser-induced isomerization which may be interpreted as coherent control of competing pump-dump and two interfering non-radiative decay processes. (C) 2008 Elsevier B.V. All rights reserved.