OBSERVATION OF STRONG CORIOLIS COUPLING IN THE INFRARED-SPECTRUM OF AR-CO

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 21 57 cm(-1) region. 47 new lines of the parallel transition from the K-a = 1 (v(CO) = 0) ground state to the combination band of the CO fundam ental vibration (v(CO) = 1) and the excited bending K-a = 1 (j = 2) st ate were assigned. The lower state is identical to that found by McKel lar er 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 (v(CO) = 1, j = 1) state. Due to a strong Coriolis intera ction 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 assig ned as containing both j = 2 (doubly excited bending) and j = 0 (van d er Waals stretching mode) contributions. These experimental results pr ovide a sensitive test of the depth and the anisotropic part of the in termolecular potential surface of Ar-CO and will be of great value for future ab initio calculations.