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- Title
Ab initio studies of the van der Waals complex CH<sub>4</sub>-O<sub>2</sub>. CH···O and CX···O interactions in halomethane X<sub>n</sub>CH<sub>4−n</sub>-O<sub>2</sub> complexes (X = F, Cl; n = 1, 2, 3)
- Authors
Grein, Friedrich
- Abstract
Using the explicitly correlated CCSD(T)-F12b method with cc-pVXZ-F12 basis sets up to X = 4, geometries for various configurations of the triplet CH4-O2 van der Waals complex were optimized. Counterpoise-corrected geometries and energies were obtained, and extrapolations to the complete basis set (CBS) limit were performed. Accordingly, the most stable isomer of the complex has O2 T-shaped facing CH3 (De = 183 cm−1, CBS value), followed by O2 T-shaped in plane with CH2 (157 cm−1), being more stable than lying perpendicular to this plane (142 cm−1). The linear HCH3-OO structure is similarly stable (138 cm−1), whereas linear H2CH2-OO is less stable (115 cm−1). Structures with O2 facing CH have the lowest stability. Harmonic frequencies point to a stable HCH3-O2 complex, with CH4 and O2 frequencies slightly red shifted. Binding energies of the various structures can be related to the number of weak intermolecular C-H···O interactions. Comparisons with the literature results for CH4-N2, CH4-NO, and CH4-CO complexes are made. Complexes of fluoromethanes and chloromethanes with O2 in linear C···OO arrangements were studied at the cc-pVDZ-F12 level. Any substitution increases the stability of the complex over the methane values. Complexes of CHF3-OO and CHCl3-OO, with three halogens facing O2, are most stable.
- Subjects
VAN der Waals forces; HALOMETHANES; METHANE; HALOGENS; ISOMERS
- Publication
Theoretical Chemistry Accounts: Theory, Computation, & Modeling, 2018, Vol 137, Issue 5, p1
- ISSN
1432-881X
- Publication type
Article
- DOI
10.1007/s00214-018-2250-z