An investigation of three-body effects in intermolecular forces. III. Far infrared laser vibration–rotation–tunneling spectroscopy of the lowest internal rotor states of Ar2HCl

The c-type intermolecular out-of-plane bend of Ar2HCl has been observed at 45.2 cm−1, completing the high resolution far infrared measurements of the three lowest-lying Ar2HCl bending states which correlate to the j=1 internal rotational state of the HCl monomer. The rotational and nuclear quadrupole hyperfine structures indicate the existence of a Coriolis perturbation. The perturbing state is postulated to be a heavy-atom stretching overtone that is very nearly degenerate with the out-of-plane bend. A partial reassignment of the previously reported [J. Chem. Phys. 95, 3182 (1991)] Ar2HCl in-plane bend is presented and a treatment of Coriolis effects between the in-plane and Σ bends is discussed. Comparison with dynamically rigorous calculations presented in the accompanying paper [J. Chem. Phys. 98, 5337 (1993)] indicate substantial three-body contributions to the intermolecular potential, which should be determinable from the data presented in this paper.