Ab initio studies of the van der Waals complex CH4-O-2 center dot CH center dot center dot center dot O and CX center dot center dot center dot O interactions in halomethane XnCH4-n-O-2 complexes (X = F, Cl; n=1, 2, 3)

作者：Grein Friedrich^*

来源：Theoretical Chemistry Accounts, 2018, 137(5): 70.

DOI：10.1007/s00214-018-2250-z

• CH4-O-2 complex
• CCSD(T)-F12 method
• Complete basis set limit
• Counterpoise correction
• Harmonic frequencies
• Complexes of O-2 with halomethanes

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-O-2 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 O-2 T-shaped facing CH3 (D-e = 183 cm(-1), CBS value), followed by O-2 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 O-2 facing CH have the lowest stability. Harmonic frequencies point to a stable HCH3-O-2 complex, with CH4 and O-2 frequencies slightly red shifted. Binding energies of the various structures can be related to the number of weak intermolecular C-H center dot center dot center dot O interactions. Comparisons with the literature results for CH4-N-2, CH4-NO, and CH4-CO complexes are made. Complexes of fluoromethanes and chloromethanes with O-2 in linear C center dot center dot center dot 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 O-2, are most stable.

• 出版日期2018-5-2