Knowledge Bank

The dimeric complexes, CH$3$OH-CO$2$ and CH$3$OH-H$2$CO, were observed with pulsed-beam Fourier transform spectrometers at NIST. For the formaldehyde complex a heated reservoir nozzle was emploved and pressurized with a gas sample of 1% methanol in either Ne or Ar carrier and the nozzle heated to about 75 . For the CO$2$ complex, a cylinder containing 1% methanol and 1% CO$2$ in Ar was used with a room temperature nozzle. Measurements were carried out from 8 GHz to 23 GHz. Both complexes exhibited internal rotation splitting due to internal rotation of the methyl group, and the formaldehyde complex showed an additional splitting on b-type transitions which is interpreted as a C$2$ tunneling motion of the H$2$CO monomer. Several isotopically substituted forms have also been studied for improved structure determination. The CO$2$ complex is van der Waals bonded (C of carbon dioxide to O of the methanol), while the formaldehyde complex is hydrogen bonded (H of the hydroxyl group to O of formaldehyde). Discussion of the rotational, Stark, internal rotation, and structure analyses will be presented. These results will be compared to ab initio calculations, as well.