Infrared spectroscopy of ArOH:: A direct probe of the Ar plus OH X2Π potential energy surface

An infrared-ultraviolet (IR-UV) double-resonance technique has been implemented to obtain the infrared spectrum of ArOH in the vicinity of the fundamental OH stretch at 2.8 mu m. A rotationally resolved spectrum of the fundamental OH stretching band of ArOH is observed at 3567.85(1) cm(-1) (origin). A combination band, involving both OH stretch and intermolecular bending excitation, is identified at 3577.00(1) cm(-1) (origin). The intermolecular energy of the excited bending state provides a direct measure of the anisotropy of the Ar+OH X(2)Pi interaction potential. The rotational structure of the combination band reveals a large splitting between parity components with the same total angular momentum in the excited bending state [0.69(1) cm-1 for J=3/2]. The experimentally derived parity splitting is compared with previous experimental and theoretical determinations of this parameter. The parity splitting associated with the excited bending state reflects the change in the intermolecular potential when the p pi orbital containing the unpaired electron of OH lies in or out of the ArOH plane. (C) 2000 American Institute of Physics. [S0021-9606(00)01111-9].