Infrared spectra of He–, Ne–, and Ar–C6D6

Spectra of He–, Ne– and Ar–C6D6 in the region of the ν12 fundamental of C6D6 are observed in a pulsed supersonic jet expansion using a tunable optical parametric oscillator laser source. These are the first reported infrared spectra of rare gas–benzene complexes and the first observation in any region for He– and Ne–C6D6. Two bands are studied for each complex: the ν12 fundamental itself (≈2289 cm−1) and the ν2 + ν13 combination band (≈2276 cm−1) which are coupled by a Fermi resonance. Effective intermolecular separations of 3.593(1) and 3.455(1) Å are obtained for He– and Ne–C6D6, respectively, consistent with previous ultraviolet and microwave results for the analogous C6H6 complexes.