O2-Dependence of reactions of 1,2-dimethoxyethanyl and 1,2-dimethoxyethanylperoxy isomers

Reaction mechanisms of R-center dot and ROO center dot radicals derived from low-temperature oxidation of 1,2-dimethoxyethane (CH3O(CH2)(2)OCH3) were investigated using speciation from multiplexed photoionization mass spectrometry (MPIMS) measurements via Cl-initiated oxidation, in conjunction with electronic structure calculations. The experiments were conducted at 5 bar, from 450 K - 650 K, and O-2 concentrations from 1 <middle dot> 10(14) cm(-3) - 6 <middle dot> 10(18) cm(-3) to probe the effects on competing reaction channels of 1,2-dimethoxyethanyl (R-center dot) and 1,2-dimethoxyethanylperoxy (ROO center dot) isomers. Several species were detected with photoionization spectral fitting - ethene, formaldehyde, methyl vinyl ether, and 2-methoxyacetaldehyde - and, as determined by electronic structure calculations, may form via unimolecular decomposition of 1,2-dimethoxyethanyl or 1,2-dimethoxyethanylperoxy. O-2-dependent yield ratios show that the formation pathways for all species undergo a competition between O-2-addition and unimolecular decomposition. Adiabatic ionization energies were also calculated and utilized along with exact mass determinations to infer contributions for other species derived exclusively from first- and second-O-2-addition, including 1,2-dimethoxyethene, cyclic ethers, and dicarbonyls. In addition to species formed from conventional low-temperature oxidation pathways, an important conclusion is derived from the detection of species produced from an O-2-addition step involving & Cdot;H2CH2OCH3 (R-center dot '), which forms via prompt dissociation of the primary 1,2-dimethoxyethanyl radical (& Cdot;H2O(CH2)(2)OCH3). Species derived from R-center dot ' + O-2 - 1,3-dioxolane and methyl acetate - were detected at [O-2] = 1.2 <middle dot> 10(17) cm(-3) and formed on timescales parallel to the main R-center dot + O-2 reactions. In addition, ion signal at m/z 106 was detected and increased with O-2 concentration from which connections are drawn to ketohydroperoxides produced by Q(center dot)' OOH + O-2. Detection of such species indicate that beta-scission of 1,2-dimethoxyethanyl is sufficiently facile such that timescales of R-center dot ' + O-2 compete with conventional R-center dot + O-2 pathways.