Weakly exothermic rearrangement of methoxy radical (CH/sub 3/O/sup center-dot/) to the hydroxymethyl radical (CH/sub 2/OH/sup center-dot/)
Although the CH/sub 3/O/sup center-dot/ and CH/sub 2/OH/sup center-dot/ radicals have long been considered critical intermediates in combustion and atmospheric processes, only very recently has the potential significance of the isomerization CH/sub 3/O/sup center-dot/..-->..CH/sub 2/OH/sup center-dot/ been appreciated. This isomerization and related aspects of the CH/sub 3/O/sup center-dot//CH/sub 2/OH/sup center-dot/ potential surface have been studied here using nonempirical molecular electronic structure theory with moderately large basis sets and with incorporation of electron correlation. The vibrational frequencies of CH/sub 3/O/sup center-dot/, CH/sub 2/OH/sup center-dot/ and seven other stationary points on the potential energy hypersurface have been predicted, both to compare with results from spectroscopy and to provide estimates of zero-point vibrational corrections. In general, there is reasonable agreement with those vibrational frequencies of CH/sub 3/O/sup center-dot/ and CH/sub 2/OH/sup center-dot/ which are known from experiment. Our ab initio calculations predict that CH/sub 3/O/sup center-dot/ lies 5.0 kcal mol/sup -1/ higher in energy than CH/sub 2/OH/sup center-dot/ with a barrier to rearrangement to CH/sub 2/OH/sup center-dot/ of 36.0 kcal mol/sup -1/. Rearrangement of CH/sub 3/O/sup center-dot/ to CH/sub 2/OH/sup center-dot/ via a dissociation--recombination mechanism is energetically more costly (by 6.1 kcal mol/sup -1/). The Jahn--Teller distortion of CH/sub 3/O/sup center-dot/ from point group C/sub 3v/ is described in some detail. Barriers to inversion and rotation in CH/sub 2/OH/sup center-dot/ are predicted and compared with the results of ESR experiments. Finally, the dissociation of CH/sub 3/O/sup center-dot/ and CH/sub 2/OH/sup center-dot/ to yield formaldehyde plus H/sup center-dot/ are each predicted to involve modest reverse activation energies.
- Research Organization:
- Research School of Chemistry, Australian National University, Canberra, A. C. T. 2600, Australia
- OSTI ID:
- 6537649
- Journal Information:
- J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 78:2; ISSN JCPSA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400301* -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
ALKOXY RADICALS
CHEMICAL REACTIONS
COMBUSTION
CORRELATIONS
DISSOCIATION
ELECTRON CORRELATION
ELECTRONIC STRUCTURE
ENERGY LEVELS
EXCITED STATES
ISOMERIZATION
METHOXY RADICALS
OXIDATION
RADICALS
THERMOCHEMICAL PROCESSES
VIBRATIONAL STATES