A Pump & Dump & Probe Strategy for the Spectroscopy of the Transition State During a Laser-Controlled Isomerization: Model Simulation for the Cope Rearrangement of 2,6-Dicyanoethylmethylsemibullvalene

摘要

Our previous strategy for laser control of isomerization by intense ultrashort (ps) infrared laser pulses is extended to the spectroscopy of the transition state during the laser-driven chemical reaction, by means of a pump & dump & probe approach. The pump laser pulse excites a reactant state, typically the ground state, to a delocalized "transition state" with energy just above the shallow potential barrier which separates the potential wells of two near-degenerate isomers. The dump 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 induces 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 of 2,6-Dicyanoethylmethylsemibullvalene (DEM-SBV) by means of representative time-dependent wave-packets. This example is used for a discussion of the new pump & dumb & probe method.