Ultrafast transient absorption spectroscopy is used to investigate of electronic and nuclear rearrangement and energy redistribution in condensed phase chemical reactions of simple molecular systems. Studies of well defined simple systems permit connections to be drawn between the elegant advances that have been made in understanding reaction mechanisms in isolated molecules and reaction mechanisms in the "real world" of condensed phase environments.
Recent work in our group has emphasized studies of the photochemical ring-opening reaction producing hexatriene from cyclohexadiene. UV excitation of cyclohexadiene results in subpicosecond ground state recovery and picosecond vibrational relaxation.
Excitation of tZt-HT results in fast internal conversion and recovery to ground state. A small population is trapped as cZt-HT and decays on a timescale of a few hundred ps.
This relaxation of hot Z-HT at early times and the thermal isomerization of cZt-HT to tZt-HT provide an interesting system to investigate the influence of solvent on molecular rearrangement.
Excitation of CHD also results in ultrafast ring-opening and internal conversion to the ground state.
The relaxation of hot Z-HT at early times following excitation of CHD provides another prospective on the influence of solvent on molecular rearrangement reactions.
In a second project, photoexcitation of alkylcobalamins is being used to produce radical pairs. Transient absorption spectroscopy is then used to investigate the influence of the solvent on the branching between recombination and cage escape of the geminate radical pair.
This research is supported by the National Science Foundation through Grant CHS - 0078972
