THE MICROWAVE ROTATIONAL SPECTRUM OF THE AR-CO DIMER

Pure rotational spectra of four different isotopomers of the dimer Ar-CO have been investigated between 8 and 18 GHz using a pulsed beam cavity Fourier transform spectrometer. The spectra confirm that the complex is a prolate near-symmetric rotor with an essentially T-shaped structure, and that it undergoes large amplitude zero-point motion. It is shown that on the average the argon is closer to the oxygen than to the carbon. The transitions measured obey a-type selection rules with DELTAJ = + 1, DELTAK(a) = 0, and DELTAK(c) = + 1. For Ar-40-(CO)-C-13-O-16, transitions have been observed for K(a) = 0 and 1 with lower state J values of 1, 2, and 3. For Ar-40-(CO)-C-13-O-16, and Ar-40-(CO)-C-13-O-18, a similar series was measured, but only for Ka = 0. For Ar-40-(CO)-C-13-O-17, the O-17 quadrupole hyperfine pattern was resolved in the rotational transition J(KaKc) = 2(02)-1(01). Determinations have been made for rotational and centrifugal distortion constants, as well as for the 170 quadrupole coupling constant chi(aa). Effective values have been obtained for the length of the line from the center of mass of the CO subunit to the argon nucleus, and for the angle between this line and the CO bond.