Rotational study of the CH{sub 4}–CO complex: Millimeter-wave measurements and ab initio calculations

• Published in: The Journal of chemical physics 2015-10, Vol.143 (15)
• Main Authors: Surin, L. A., Institute of Spectroscopy, Russian Academy of Sciences, Fizicheskaya St. 5, 142190 Troitsk, Moscow, Tarabukin, I. V., Panfilov, V. A., Schlemmer, S., Kalugina, Y. N., Faure, A., Rist, C., CNRS, IPAG, F-38000 Grenoble, Avoird, A. van der
• Format: Article
• Language: English
• Subjects: BINDING ENERGY; CARBON MONOXIDE; COMPARATIVE EVALUATIONS; COMPLEXES; DISSOCIATION ENERGY; EXCITATION; EXCITED STATES; GROUND STATES; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; MATHEMATICAL METHODS AND COMPUTING; METHANE; POTENTIAL ENERGY; SPECTRA; SPIN; VAN DER WAALS FORCES
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.4933061

The rotational spectrum of the van der Waals complex CH{sub 4}–CO has been measured with the intracavity OROTRON jet spectrometer in the frequency range of 110–145 GHz. Newly observed and assigned transitions belong to the K = 2–1 subband correlating with the rotationless j{sub CH4} = 0 ground state and the K = 2–1 and K = 0–1 subbands correlating with the j{sub CH4} = 2 excited state of free methane. The (approximate) quantum number K is the projection of the total angular momentum J on the intermolecular axis. The new data were analyzed together with the known millimeter-wave and microwave transitions in order to determine the molecular parameters of the CH{sub 4}–CO complex. Accompanying ab initio calculations of the intermolecular potential energy surface (PES) of CH{sub 4}–CO have been carried out at the explicitly correlated coupled cluster level of theory with single, double, and perturbative triple excitations [CCSD(T)-F12a] and an augmented correlation-consistent triple zeta (aVTZ) basis set. The global minimum of the five-dimensional PES corresponds to an approximately T-shaped structure with the CH{sub 4} face closest to the CO subunit and binding energy D{sub e} = 177.82 cm{sup −1}. The bound rovibrational levels of the CH{sub 4}–CO complex were calculated for total angular momentum J = 0–6 on this intermolecular potential surface and compared with the experimental results. The calculated dissociation energies D{sub 0} are 91.32, 94.46, and 104.21 cm{sup −1} for A (j{sub CH4} = 0), F (j{sub CH4} = 1), and E (j{sub CH4} = 2) nuclear spin modifications of CH{sub 4}–CO, respectively.