Millimeter-wave study of the CH4–CO complex: New measurements with OROTRON spectrometer

Abstract The pure rotational spectrum of the van der Waals complex, CH 4 –CO, has been measured using the intracavity OROTRON jet spectrometer in the frequency range of 116–146 GHz. The newly observed and assigned transitions belong to the R -branch with J numbers from 9 to 16 of the K  = 1–0 sub-band. This series is a continuation to higher J -values of transitions correlating with the rotationless j M  = 0 state ( A symmetry state) of free methane observed previously at lower frequencies [C. Xia, K.A. Walker, A.R.W. Mckellar, J. Chem. Phys. 114 (2001) 4824]. Both data sets were analyzed together with known infrared and microwave transitions in order to determine the molecular parameters of the of CH 4 –CO complex in the A state. The observed millimeter-wave spectrum shows numerous additional transitions which very likely belong to CH 4 –CO composed of methane in the F ( j M =  1) and E ( j M =  2) symmetry states, but these have not yet been assigned.