Laser-driven Ultrafast Hydrogen Transfer Dynamics

Laser-driven Ultrafast Hydrogen Transfer Dynamics 

The first question, which is raised by this simple analogy, concerns the very possibility of exciting slow mode wave packets in a hydrogen bond at all. Taking a different perspective it touches the very issue of interpretation of the notoriously complex IR spectra [9]. In the condensed phase much of this complexity is hidden under bands broadened by the solvent interaction. Hence it was only recently that coherent wave packet motion of a 100 cm i hydrogen bond mode could be observed after OH-stretch excitation, although in a system which has only a single minimum potential [10]. Meanwhile coherent low-frequency dynamics has also been observed in a double minimum system (acetic acid dimer) [11]. With this 

Hydrogen-Transfer Reactions. Edited by J. T. Hynes, J. P. Klinman, H. H. Limbadi, and R. L. Schowen Copyright 2007 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 978-3-527-30777-7 

Two scenarios for H-bond dynamics will be addressed below First, IR laser control of HT between different tautomers in the electronic ground state second, H-bond breaking by combining IR pre-excitation with a second UV pulse which switches the electronic state. In both cases short few-cycle IR pulses will play an important role. 

If one aims to explore the PES this approach is rather illuminating. For dynamics calculations, however, one faces the challenge that due to the curvilinear nature of the coordinates, the kinetic energy operator takes a rather complicated form. This necessitates further approximations such as the adiabatic decoupling between the reaction coordinates and the orthogonal oscillator modes. It is probably because of this difficulty that the approach has not been fully explored for the use in HT reaction dynamics for many years. It has been only recently that interest has been revived and a number of studies focused on this approach [23-26]. 

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Laser-driven Ultrafast Hydrogen Transfer Dynamics... 

In Ch. 4, Kiihn and Gonzalez deals with the theory of ultrafast hydrogen transfer dynamics driven by tailored IR laser pulses. For small systems such as OHF pulse schemes can be devised, which either lead to a breaking of the OH or of the HF bond. For multidimensional hydrogen bond dynamics in medium sized mole-... 

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