Spectroscopic observation of isomerization kinetics in isotopically labeled (benzene)(13)

Isotopically labeled (benzene)(13) clusters, (C6H6)(C6D6)(12), generated in supersonic expansion, were studied by resonance-enhanced two-photon ioniza tion (R2PI) spectroscopy as a function of nozzle-to-laser distance using tw o distinct sets of expansion conditions. In this report we present spectros copic evidence for both evaporation and isomerization within the supersonic jet. The observed (C6H6)(C6D6)12 population initially undergoes a fluxiona l-to-rigid transition; this transition is followed by isomerization within a subpopulation of the ordered, rigid clusters, in which the unique C6H6 mo iety migrates from the surface to the interior of an otherwise homogeneous C6D6 cluster. These experiments are unique in that analogous isomerization dynamics have never before been spectroscopically observed. The observed ki netics are generally insensitive to differences between the benzene:helium ratio in the expansion mixture.