Laser driven hydrogen tunneling in a dissipative environment

The recently proposed tunneling approach (N. Doslic, O. Kuhn, J. Manz, K. S undermann, J. Phys. Chem. A, in press) by which isomerization reactions can be controlled using ultrafast laser pulses is extended to incorporate envi ronmental effects. Multilevel Redfield theory is used to show how phase and energy relaxation resulting from the interaction between system and bath c oordinates leads to a deterioration of the controllability of the system's dynamics. In the tunneling approach the tunneling time between the energeti cally lowest reactant and product states sets the time scale for the contro l of isomerization. Therefore, for systems having a high barrier the time r equired for completing the reaction increases considerably. Optimal control theory applied to this case suggests the participation of excited vibratio nal states in the isomerization process. This leads us to a simple analytic al two-pulse scheme where the first pulse induces a vibrational excitation of the reactant and the second pulse drives the tunneling to the product co nfiguration. The influence of dissipation on the resulting dynamics is disc ussed. (C) 1999 Elsevier Science B.V. All rights reserved.