Infrared spectrum of the CO-OCS van der Waals complex in the carbon monoxide stretching band

The rotation-vibration band of the weakly bound OCS-CO complex which corresponds to the carbon monoxide CO vibrational mode has been detected using a pulsed supersonic slit-jet expansion and a tunable infrared diode laser probe. The band was found to have a parallel (δK _a = 0) structure, in good agreement with previous determinations of the structure of the complex. Its rotational structure appeared to be affected by numerous small (～ 0.01 cm^?1) perturbations in the upper state which probably are due to interactions with bound levels of a lower lying vibrational state of the complex. The band origin is located with a relatively small shift of + 1.23 cm^?1 from that of the free CO molecule.