The infrared spectra of C6D6-Rg1,2 complexes were observed, with the rare gas (Rg) being
He, Ne, Ar. The spectra were observed at a resolution of ~ 60 MHz using a tunable optical
parametric oscillator (OPO) to probe a pulsed supersonic-jet expansion from a slit nozzle.
The detection system also used a balanced subtraction technique to suppress the power
fluctuations inherent to the OPO. Due to a strong Fermi resonance in the C6D6 monomer,
two bands were observed for each of the complexes, one around the vibrational fundamental
of ν12 (~2289 cm-1) and other around the combination band ν2 + ν13 (~2275 cm-1) of the
benzene monomer. In the case of C6D6-Rg dimers, spectra were assigned to a symmetric
top with C6v symmetry with the rare gas atom being located on the C6 symmetry axis.
To observe the C6D6-Rg2 trimers, the nozzle had to be cooled, resulting in spectra with a
lower rotational temperature. The spectra of the C6D6-Rg2 trimers were in agreement with
a D6h symmetry structure, where the rare gas atoms are positioned on the C6 symmetry
axis, above and below the C6D6 plane.