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Title: Theoretical spectroscopic characterization at low temperatures of S-methyl thioformate and O-methyl thioformate

Highly correlated ab initio methods are employed to determine spectroscopic properties at low temperatures of two S-analogs of methyl formate: S-methyl thioformate CH{sub 3}-S-CHO (MSCHO) and O-methyl thioformate CH{sub 3}-O-CHS (MOCHS). Both species are detectable and they are expected to play an important role in Astrochemistry. Molecular properties are compared with those of the O-analog, methyl formate. Both isomers present two conformers cis and trans. cis-CH{sub 3}-S-CHO represents the most stable structure lying 4372.2 cm{sup −1} below cis-CH{sub 3}-O-CHS. The energy difference between the cis and trans forms is drastically lower for MSCHO (1134 cm{sup −1}) than for MOCHS (1963.6 cm{sup −1}). Harmonic and anharmonic fundamentals and the corresponding intensities, as well as the rotational constants for the ground vibrational and first excited torsional states and the centrifugal distortions constants, are provided. Low torsional energy levels have been obtained by solving variationally a two dimensional Hamiltonian expressed in terms of the two torsional degrees of freedom. The corresponding 2D potential energy surfaces have been computed at the CCSD(T)/aug-cc-pVTZ level of theory. The methyl torsional barriers V{sub 3}(cis) are determined to be 139.7 cm{sup −1} (CH{sub 3}-S-CHO) and 670.4 cm{sup −1} (CH{sub 3}-O-CHS). The A/E splitting of ground torsional state hasmore » been estimated to be 0.438 cm{sup −1} for CH{sub 3}-S-CHO and negligible for CH{sub 3}-O-CHS.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5]
  1. Departamento de Química y Física Teóricas, Instituto de Estructura de la Materia, IEM-C.S.I.C., Serrano 121, Madrid 28006 (Spain)
  2. Dipartimento di Chimica G. Ciamician, Università di Bologna, Via F. Selmi 2, I-40126 Bologna (Italy)
  3. Laboratoire de Modélisation et Simulation Multi Echelle, Université Paris-Est, MSME UMR 8208 CNRS, 5 boulevard Descartes, 77454 Marne-la-Vallée (France)
  4. Departamento de Ingeniería Civil, Cátedra de Química, E.U.I.T. Obras Públicas, Universidad Politécnica de Madrid, Madrid (Spain)
  5. Departamento de Física Aplicada, Facultad de Ciencias Experimentales, Unidad Asociada IEM-CSIC-U.Huelva, Universidad de Huelva, 21071 Huelva (Spain)
Publication Date:
OSTI Identifier:
22308366
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 141; Journal Issue: 10; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; COMPARATIVE EVALUATIONS; DEGREES OF FREEDOM; ENERGY LEVELS; FORMATES; HAMILTONIANS; ISOMERS; POTENTIAL ENERGY; SURFACES; TWO-DIMENSIONAL CALCULATIONS