MILLIMETER-WAVE SPECTRUM OF THE AR-CO COMPLEX - THE K=2[-1 AND 3[-2 SUBBANDS

The K-a = 2 <-- 1 and 3 <-- 2 subbands of the pure rotational spectrum of the weakly bound van der Waals complex Ar-CO have been studied by direct absorption of millimetre and submillimetre radiation in a super sonic jet. A. total of 77 transitions were observed in the 138-265 GHz (2 <-- 1 band) and 308-361 GHz (3 <-- 2 band) regions. These transiti ons were incorporated in a global ht of existing infrared, microwave a nd millimetre-wave data in order to determine a refined set of molecul ar parameters for Ar-CO. It was found that the form of the simple Hami ltonian used for this fit had to be modified, so that the rotational d ependence of the K-type splitting terms was given by (J + K)!/(J - K)! , in order to fit accurately the asymmetry doubling of the K-a = 3 lev els for lower J values. The theory of the splitting terms is explained in some detail. The present results provide a more precise foundation on which to base the continuing study of the fundamental complex Ar-C O.