engleski

The "hydrogen-subway" - A tunneling approach to intramolecular hydrogen transfer reactions controlled by ultrashort laser pulses

Isomerization reactions from a reactant state to a near-degenerate product state which are typical for intramolecular hydrogen transfer may be achieved by means of ultrashort picosecond or sub-picosecond laser pulses having three consecutive time domains: Initially, the laser field is switched on such that the wave packet representing the reactant is converted into a superposition of near-degenerate delocalized states of the "dressed" molecule In the second stage, the laser field is kept approximately constant until the wave packet has tunneled from the reactant to the product configuration, during the tunneling time. Finally the field is switched off such that the wave packet is stabilized as the target product state. This approach is suggested by optimal control theory and applied to a one--dimensional model resembling substituted malonaldehydes. Here it is found that the laser driven tunneling requires time--integrated laser field intensities fifty times smaller than the alternative pump--dump approach which drives the reactant wave packet over the potential barrier towards the product state without tunneling. Various applications and extensions of this method are discussed.

quantum dynamics; field; spectroscopy

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