The microwave rotational spectrum of the Ar–CO dimer

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Abstract
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 transformspectrometer. 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 ΔJ=+1, ΔK a =0, and ΔK c =+1. For 40Ar–12C16O, transitions have been observed for K a =0 and 1 with lower state J values of 1, 2, and 3. For 40Ar–13C16O and 40Ar–13C18O, a similar series was measured, but only for K a =0. For 40Ar–13C17O, the 17O quadrupolehyperfine pattern was resolved in the rotational transition J K aK c = 202–101. Determinations have been made for rotational and centrifugal distortion constants, as well as for the 17O quadrupole coupling constant χ 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.