Knowledge Bank

The rotational spectrum of $CH3OH-CO$ has been observed in the 7-18 GHz region with a pulsed beam Fabry-Perot cavity Fourier transform microwave spectrometer. The measurement precision and accuracy is estimated to be 4 kHz. In order to obtain detailed structural information the spectra of $CH3OH,CH3OD,CD3OH$ and $CD3OD$ complexed with $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}CO$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}CO$ were examined. Each of the isotopic species 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 verified by observing their first-order Stark effect. The spectra were analyzed using the IAM method. Only a small change in the value of the barrier to the internal rotation was found for the different species, suggesting that a possible second large-amplitude motion (overall rotation of the CO subunit) can be neglected at the present stage of the experimental data set. The structure of the complex involves planar heavy atoms and a bent hydrogen bond to the carbon atom of CO at a distance of 2.43 A from the hydroxyl hydrogen of methanol.