Infrared spectra of (H₂)₁,₂-C₆D₆ and Rg₁,₂-C₆D₆ complexes, Rg = He, Ne, Ar

Spectra of dimers and trimers containing C₆D₆ and He, Ne, Ar, or H₂ are observed in the region of the C₆D₆ ν₁₂ fundamental using a pulsed supersonic jet expansion and a tunable optical parametric oscillator laser source. These are the first reported infrared spectra of hydrogen – benzene complexes. Two bands coupled by anharmonic resonance are studied for each complex: the ν₁₂ fundamental itself (≈2289 cm⁻¹) and the ν₂ + ν₁₃ combination band (≈2276 cm⁻¹). Vibrational shifts for the trimers are found to be approximately twice those of the corresponding dimer. Effective intermolecular separations for (H₂)₁,₂-C₆D₆ are about 3.46 Å, similar to those determined previously from electronic spectra of (H₂)₁,₂-C₆H₆ and also similar to (Ne)₁,₂-C₆D₆.