Rotational study of the CH4-CO complex: Millimeter-wave measurements and ab initio calculations.
The rotational spectrum of the van der Waals complex CH4-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 jCH4 = 0 ground state and the K = 2-1 and K = 0-1 subbands correlating with the jCH4 = 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 CH4-CO complex. Accompanying ab initio calculations of the intermolecular potential energy surface (PES) of CH4-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 CH4 face closest to the CO subunit and binding energy De = 177.82 cm(-1). The bound rovibrational levels of the CH4-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 D0 are 91.32, 94.46, and 104.21 cm(-1) for A (jCH4 = 0), F (jCH4 = 1), and E (jCH4 = 2) nuclear spin modifications of CH4-CO, respectively.
I. Physikalisches Institut, University of Cologne, Zülpicher St. 77, 50937 Cologne, Germany.
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Surin
Institute of Spectroscopy, Russian Academy of Sciences, Fizicheskaya St. 5, 142190 Troitsk, Moscow, Russia.
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Tarabukin
Institute of Spectroscopy, Russian Academy of Sciences, Fizicheskaya St. 5, 142190 Troitsk, Moscow, Russia.
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Panfilov
I. Physikalisches Institut, University of Cologne, Zülpicher St. 77, 50937 Cologne, Germany.
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Schlemmer
Department of Optics and Spectroscopy, Tomsk State University, 36 Lenin Ave., 634050 Tomsk, Russia.
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Kalugina
University Grenoble Alpes, IPAG, F-38000 Grenoble, France.
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Faure
University Grenoble Alpes, IPAG, F-38000 Grenoble, France.
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Rist
Theoretical Chemistry, Institute for Molecules and Materials, Radboud University, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands.
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van der Avoird