title: Accurate ab initio vibrational energies of methyl chloride.
abstract: Two new nine-dimensional potential energy surfaces (PESs) have been generated using high-level ab initio theory for the two main isotopologues of methyl chloride, CH3 (35)Cl and CH3 (37)Cl. The respective PESs, CBS-35( HL), and CBS-37( HL), are based on explicitly correlated coupled cluster calculations with extrapolation to the complete basis set (CBS) limit, and incorporate a range of higher-level (HL) additive energy corrections to account for core-valence electron correlation, higher-order coupled cluster terms, scalar relativistic effects, and diagonal Born-Oppenheimer corrections. Variational calculations of the vibrational energy levels were performed using the computer program TROVE, whose functionality has been extended to handle molecules of the form XY 3Z. Fully converged energies were obtained by means of a complete vibrational basis set extrapolation. The CBS-35( HL) and CBS-37( HL) PESs reproduce the fundamental term values with root-mean-square errors of 0.75 and 1.00 cm(-1), respectively. An analysis of the combined effect of the HL corrections and CBS extrapolation on the vibrational wavenumbers indicates that both are needed to compute accurate theoretical results for methyl chloride. We believe that it would be extremely challenging to go beyond the accuracy currently achieved for CH3Cl without empirical refinement of the respective PESs.
authors.affiliation: Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany.
authors.forename: Alec
authors.initials: A
authors.lastname: Owens
authors.affiliation: Department of Physics and Astronomy, University College London, Gower Street, WC1E 6BT London, United Kingdom.
authors.forename: Sergei N
authors.initials: SN
authors.lastname: Yurchenko
authors.affiliation: Department of Physics and Astronomy, University College London, Gower Street, WC1E 6BT London, United Kingdom.
authors.forename: Andrey
authors.initials: A
authors.lastname: Yachmenev
authors.affiliation: Department of Physics and Astronomy, University College London, Gower Street, WC1E 6BT London, United Kingdom.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Tennyson
authors.affiliation: Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany.
authors.forename: Walter
authors.initials: W
authors.lastname: Thiel
mesh_terms: D004583:Electrons; D008737:Methyl Chloride / Q000737:chemistry*; D011789:Quantum Theory; D013816:Thermodynamics; D014732:Vibration
chemical_list: D008737:Methyl Chloride