Abstract
The present study aims at a fundamental understanding of bonding characteristics of the C–Br and O–Br bonds. The target molecular systems are the isomeric CH3OBr/BrCH2OH system and their decomposition products. Calculations of geometries and frequencies at different density functional theory (DFT) and Hartree–Fock/Møller–Plesset (HF/MP2) levels have been performed. Results have been assessed and evaluated against those obtained at the coupled cluster single-double (Triplet) (CCSD(T)) level of theory. The characteristics of the C–Br and O–Br bonds have been identified via analysis of the electrostatic potential, natural bond orbital (NBO), and quantum theory of atoms in molecules (QTAIM). Analysis of the electrostatic potential (ESP) maps enabled the quantitative characterization of the Br σ-holes. Its magnitude seems very sensitive to the environment and the charge accumulated in the adjacent centers. Some quantum topological parameters, namely ∇2ρ, ellipticity at bond critical points and the Laplacian bond order, were computed and discussed. The potential energy function for internal rotation has been computed and Fourier transformed to characterize the conformational preferences and origin of the barriers. NBO energetic components for rotation about the C–Br and O–Br bonds as a function of torsion angle have been computed and displayed.
Highlights
The important role of bromine species in ozone depletion [1,2,3,4] in the Antarctic spring caused much research on these species in polar regions
The reaction between bromine oxides with HOx species leading to the production of methyl bromide is of particular importance in this respect [7,8,9]
Calculations at the different density functional theory (DFT) levels and at the HF-MP2 level of theory are compared to the CCSD(T) results in Table S1 of the supplementary material
Summary
The important role of bromine species in ozone depletion [1,2,3,4] in the Antarctic spring caused much research on these species in polar regions. The reaction between bromine oxides with HOx species leading to the production of methyl bromide is of particular importance in this respect [7,8,9]. This process becomes more efficient in regions with high OH concentration. The isomeric system CH3OBr/CH3BrO/BrCH2OH is suggested to play the major role in these photochemical processes, yet no systematic study of the energies, structures and dynamics of the excited states has been published. The target molecular systems are the isomeric CH3OBr/BrCH2OH system and their decomposition products which are suggested to play a major role in ozone depletion processes.
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