Microwave spectrum of the heterodimers: CH3OH-CO2 and CH3OH-H2CO

Molecular complexes, dimers and heterodimers often show interesting structures, large amplitude internal motions and orientations for reaction coordinates. These properties were the motivations for the current study of the rotational spectra of the heterodimers, CH3OH-CO2 and CH3OH-H2CO, in a pulsed nozzle Fourier-transform microwave (FTMW) spectrometer. In addition to studying the normal isotopic forms, several isotopologues containing 13C or deuterium substituted atoms of each heterodimer were analyzed in order to obtain structural data of the complexes. All species showed splittings from internal rotation of the methyl group and splittings on the b-type transitions of the CH3OH-H2CO species suggesting rotation of the H2CO group between equivalent structural forms. Stark effect measurements on each of the parent species provided dipole moment components. Theoretical ab initio results are compared to the experimentally determined molecular parameters.