PRIMARY METHOXY RADICAL FORMATION IN THE REACTION OF METHANOL VAPOR WITH Hg 6(3P1) ATOMS

A study has been made of the decomposition of methanol vapor by Hg 6(3P1) atoms, under static conditions, at 25 °C. A system constructed entirely of quartz was employed to eliminate the dark reaction between methanol vapor and pyrex glass to form trimethyl borate. Emphasis in this investigation was placed on the determination of the nature of the primary processes operative, and to this end, the reaction was studied in some detail in the presence of nitric oxide.For pure methanol, the major primary products were found to be hydrogen and ethylene glycol. The primary quantum yield for hydrogen was 0.46. Minor products of primary origin were formaldehyde (0.01), ethane (0.005), and dimethyl ether (0.006), with the numbers in parentheses showing the primary quantum yields.In the presence of nitric oxide, the major products became methyl nitrite, nitrous oxide, and water. The quantum yield of methyl nitrite rose steadily with increasing NO concentrations. For a 1:1 CH3OH:NO mixture, the primary quantum yield for methyl nitrite was found to be 0.56. The behavior of the reaction in the presence of NO establishes fairly unequivocally that the major primary process involves O—H bond scission to form methoxy radicals and H atoms. These primary radicals then form hydroxymethyl radicals by abstraction reactions with the substrate. The ethylene glycol product arises by recombination of the secondary hydroxymethyl radicals. These conclusions were further substantiated by mass spectrometric analysis of the products of the decomposition of CD3OH. It was shown that CD3OD is a significant product of the reaction.