Observation of strong Coriolis coupling in the infrared spectrum of Ar-CO

Abstract

Using a continuous two-dimensional jet expansion in combination with a computer controlled diode laser spectrometer, the rotation-vibration spectrum of the Ar-CO van der Waals complex has been studied in the 2157 cm-1 region. 47 new lines of the parallel transition from the K a = 1 (νCO = 0) ground state to the combination band of the CO fundamental vibration (νCO = 1) and the excited bending K a = 1 (j = 2) state were assigned. The lower state is identical to that found by McKellar et al. (1992, J. Molec. Spectrosc., 153, 475). The excited bending K a = 1 state is located at an energy of 14·63 cm-1 with respect to the K a = 1 (νCO = 1, j = 1) state. Due to a strong Coriolis interaction with a nearby K a = 0 state, this new band shows unusually large asymmetry splittings. Using the results of a perturbative analysis of the Coriolis coupling, the nature of the K a = 0 state could be assigned as containing both j = 2 (doubly excited bending) and j = 0 (van der Waals stretching mode) contributions. These experimental results provide a sensitive test of the depth and the anisotropic part of the intermolecular potential surface of Ar-CO and will be of great value for future ab initio calculations.