SPECTROSCOPIC EVIDENCE FOR HIGH SYMMETRY IN (BENZENE)13

The (benzene)13 cluster and its isotopic derivatives have been formed in a dilute benzene/helium jet, and investigated by mass-selective R2PI spectroscopy in the region of the B2u <-- A1g O0(0) and 6(0)1 transitions. Each band exhibits resolved fine structure, which differs greatly between forbidden (O0(0)) and allowed (6(0)1) bands. The main features, identified by spectral shift, are proposed to correspond to distinct molecular sites, whose symmetries are deduced by comparing spectra of the allowed and induced vibronic bands. The isotopic substitution of one C6H6 molecule into an otherwise deuterated cluster results in a considerable spectral simplification, due in part to highly nonrandom labelling. The results appear to rule out the crystallographic structure, while being consistent with the compact noncrystallographic structure computed by van de Waal.