Comparison of Three Isoelectronic Multiple-Well Reaction\nSystems: OH + CH₂O, OH + CH₂CH₂,\nand OH + CH₂NH

Abstract

Methylenimine\n(CH₂NH) has been predicted to be a product\nof the atmospheric photo-oxidation of methylamine, but its atmospheric\nreactions have not been measured. In this paper, we report potential\nenergy surfaces (PESs) and rate constants for OH + CH₂NH\nand its isoelectronic analogues OH + CH₂O and OH + CH₂CH₂, which are more fully understood. The PESs\nwere computed using the BHandHLYP/aug-cc-pVTZ and CCSD­(T)/aug-cc-pVTZ\nlevels of theory. Canonical variational transition state theory and\nRice–Ramsperger–Kassel–Marcus and master equation\nmodeling were used to calculate temperature- and pressure-dependent\nrate constants, with particular emphasis on the OH + reactant entrance\nchannels and the effects of prereactive complexes. The computed results\nare in reasonable agreement with experimental data where they can\nbe compared and also with the results of previous theoretical calculations.\nThe results show that to some extent OH radicals both add to the carbon\ncenter double bond in CH₂NH and abstract methylene hydrogen\natoms, as in the OH + CH₂O and OH + CH₂CH₂ reactions, respectively, but the dominant pathway is abstraction\nof the hydrogen from N–H. The computed rate constants are suitable\nfor both atmospheric and combustion modeling.