Quantum Mechanical Studies of CH₃ClO₃ Isomers and the CH₃O₂+ClO Reaction Pathways

Abstract

The geometries, harmonic vibrational frequencies, and relative energetics of CH 3 ClO 3 isomers have been examined using quantum mechanical methods. At the G2MP2 level of theory, the lowest-energy structure is found to be the CH 3 OClO 2 form followed by the chain-type CH 3 OOOCl isomer located 7.9 kcal mol -1 higher. The QCISD(T) method predicts that the CH 3 OOOCl structure is located lower than CH 3 OClO 2 . The two higher-energy structures are CH 3 OOClO and CH 3 ClO 3 across all energy levels. Interisomerization transition states have been determined, and the role of the formation of CH 3 ClO 3 structures in the various pathways of the reaction CH 3 O 2 + ClO is also examined.

A computational investigation of the atmospheric reaction CH3O2+ClO

“…TS8 is also located below reactants as already said, presenting no barrier for the isomerization CH 3 OOClO M CH 3 OClO 2 . Hence, the current calculations suggest that methyl chlorate may be formed as a reaction intermediate through either TS1 or TS8 and may participate in the mechanism of the reaction CH 3 O 2 + ClO, contrary to what has been originally assumed [10].…”

“…An important new feature in the current work is the finding that methyl chlorate, CH 3 OClO 2 , although not a nascent association minimum, may also be formed as a reaction intermediate on the singlet surface directly from the reactants, opposite to what has been previously assumed [10]. Thus, CH 3 OClO 2 may be formed either from CH 3 O 2 + ClO through the newly determined transition state TS1 or through isomerization of the methoxy chlorite isomer, CH 3 OOClO, via transition state TS8.…”

“…more stable than the former by 7.9 kcal mol À1 . Previous calculations at the QCISD(T)/6-311G(2df, 2p) level [10] have also indicated the high stability of these two isomers but they have predicted that 1 CH 3 OOOCl is more stable than CH 3 OClO 2 by 4.2 kcal mol À1 . The second association minimum, CH 3 OOClO, is found less stable than 1 CH 3 OOOCl and CH 3 OClO 2 but still lower than the reactant energy level, thus, making another possible reaction intermediate.…”

“…The only computational investigation of reaction (1) with particular emphasis on the quantum mechanical characterization of (CH 3 ClO 3 ) isomers, the most important energy minima in the potential energy surface of reaction (1), has been reported from our [10]. In that work several drawbacks have been observed, for example the main channel (1a) was calculated to present a relatively significant critical energy contrary to the experimental evidence [2,4,9].…”

Structures, Vibrational Spectra, and Relative Energetics of CH3COIO3 Isomers

“…2,6,8 These systems are analogous to the reactions of HO 2 and CH 3 O 2 with the ClO and BrO radicals for which several experimental and theoretical studies have been reported. [9][10][11] It was found that the reaction of HO 2 ＋IO 12 displayed a rate coefficient, k＝ (8.4±0.3)×10 -11 cm 3 •molecule -1 •s -1 at 298 K and Drougas et al 6 suggested that the HO 2 and IO reaction proceed through the formation of the bound complexes, HOOOI and HOOIO. Two of the experimental studies have shown that the reactions RO 2 ＋IO are fast and may indeed have an important impact on ozone chemistry.…”