Infrared and millimeter wave spectra of the CH4-CO complex in the A internal rotation state

The weakly bound van der Waals complex CH4-CO has been observed spectroscop ically for the first time in the infrared (C-O stretching, approximate to 2 143 cm(-1)) and millimeter wave (80-107 GHz) regions. The spectra analyzed here resemble quite closely those of the rare gas-carbon monoxide complexes , like Ne-CO and Ar-CO, and they almost certainly arise from CH4-CO complex es composed of CH4 in the lowest j = 0 rotational state of A symmetry. The effective ground state intermolecular separation is 3.994 Angstrom. Predict ions are given here for the K = 0 and 1 pure rotational microwave transitio ns of CH4-CO in the A state. The infrared spectrum shows numerous additiona l transitions which must be due to CH4-CO composed of methane in the F and E symmetry states, but these have not yet been assigned. Future microwave m easurements on these F and E states will aid further progress on the infrar ed spectrum. (C) 2001 American Institute of Physics.