THE MICROWAVE-SPECTRUM AND STRUCTURE OF THE CH3OH-CO DIMER

The rotational spectrum of CH3OH-CO has been observed in the region 7- 18 GHz with a pulsed-beam Fabry-Perot cavity Fourier-transform microwa ve spectrometer. In order to obtain detailed structural information th e spectra of CH3OH, CH3OD, CD3OH, and CD3OD combined with CO and (CO)- C-13 were examined. Each of the isotopic species studied exhibits two states, which are interpreted as A and E symmetry states arising from internal rotation of the methyl group. The E-state assignments were ve rified by observing their first-order Stark effect. The structure of t he complex is a bent hydrogen bond of the carbon atom of CO at a dista nce of 2.41 angstrom from the hydroxyl hydrogen of methanol and planar heavy atoms. The effective barrier to internal rotation for CH3OH-CO, V3 = 183.0 cm-1, is one-half of the value for the methanol monomer. ( C) 1994 Academic Press, Inc.