AN INVESTIGATION OF 3-BODY EFFECTS IN INTERMOLECULAR FORCES .2. FAR-INFRARED VIBRATION-ROTATION TUNNELING LASER SPECTROSCOPY OF AR2HCL

A second Ar2 HCl intermolecular vibration-rotation band centered at 37.2 cm-1 has been measured and assigned as a b-type transition originating from the ground state. Nuclear hyperfine splittings were resolved for both chlorine isotopes. The rotational constants determined from the data indicate coupling between an Ar-Ar stretching or bending coordinate and the Ar2-HCl vibrational coordinates. As a result of this particular vibrational motion, Ar2H Cl-35 undergoes an axis-switching transition while the Ar2H Cl-37 isotope does not. In addition, the measured hyperfine projections indicate the possibility of coupling between the Ar2-HCl stretching and bending modes, preventing an absolute vibrational assignment. These results indicate that the "reversed adiabatic" approximation employed by Hutson, Beswick, and Halberstadt in their theoretical study of Ar2HCl [J. Chem. Phys. 90, 1337 (1989)] is not appropriate for the complicated intramolecular dynamics presently observed in this system.