Ultrafast wave packet dynamics of an intramolecular hydrogen transfer system: From vibrational motion to reaction control

Abstract

A seven-dimensional all-Cartesian reaction surface Hamiltonian in the diabatic representation of the in-plane large amplitude hydrogen atom coordinates is employed to study the infrared (IR) spectrum and the vibrational dynamics of the hydrogen bond of deuterated salicylaldimine in the gas phase. The model Hamiltonian is related to the standard approach which incorporates low-order anharmonicities in the vicinity of a minimum on the potential energy surface. The IR spectrum is discussed on the basis of the diabatic representation paying attention to the OD stretching and bending excitations. As compared with the normal species, deuteration leads to a much simpler IR spectrum due to the shift of the relevant transitions into a region of lower density of states. As a consequence, intramolecular vibrational energy redistribution after ultrafast laser-excitation which is simulated using the multiconfiguration time-dependent Hartree method is less efficient. The persistence of coherence in the OD bond over several picoseconds suggests the application of IR laser pulse shaping methods to trigger the enol-keto tautomerism in this model system. First results focusing on the stability and the relaxation pathways out of the keto configuration are presented. © 2004 Elsevier B.V. All rights reserved.