A PUMP AND DUMP AND PROBE STRATEGY FOR THE SPECTROSCOPY OF THE TRANSITION-STATE DURING A LASER-CONTROLLED ISOMERIZATION - MODEL SIMULATION FOR THE COPE REARRANGEMENT OF 2,6-DICYANOETHYLMETHYLSEMIBULLVALENE

Our previous strategy for laser control of isomerization by intense ul trashort (ps) infrared laser pulses is extended to the spectroscopy of the transition state during the laser-driven chemical reaction, by me ans of a pump & dump & probe approach. The pump laser pulse excites a reactant state, typically the ground state, to a delocalized ''transit ion state'' with energy just above the shallow potential barrier which separates the potential wells of two near-degenerate isomers. The dum p laser pulse de-excites the transition state to a product state, e.g. its ground state. The transient population of the transition state is monitored by another ultrashort, yet weak probe laser pulse which ind uces the electronic transition to the vibrational ground state of the next accessible excited electronic state. The strategy is demonstrated by a simple model simulation of the laser-driven Cope rearrangement o f 2,6-Dicyanoethylmethylsemibullvalene (DEM-SBV) by means of represent ative time-dependent wave-packets. This example is used for a discussi on of the new pump & dumb & probe method.