Laser driven hydrogen tunneling in a dissipative environment

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