THEORY OF ULTRAFAST LASER CONTROL OF ISOMERIZATION-REACTIONS IN AN ENVIRONMENT - PICOSECOND COPE REARRANGEMENT OF SUBSTITUTED SEMIBULLVALENES

An efficient approach to control isomerization reactions by ultrashort infrared laser pulses in the presence of a thermal environment is dev eloped and demonstrated by means of model simulations within the reduc ed density matrix formalism beyond a Markov-type approximation for a p icosecond Cope rearrangement of 2,6-dicyanoethyl-methylsemibullvalene coupled to a quasi-resonant environment. The population transfer from the reactant state via the delocalized transition state to the product state is accomplished by two picosecond infrared laser pulses with a probability up to 80% despite the rather strong coupling to the enviro nment, which reduces the lifetime of the transition state into the fem tosecond time domain. Simulations, carried out for helium (4 K), nitro gen (77.2 K) and room (300 K) temperatures, show that low temperatures are preferable for state-selective laser control of isomerization rea ctions. (C) 1996 American Institute of Physics.