Proton transfer mass spectrometry studies of peroxy radicals

A laminar flow reactor coupled to a proton transfer mass spectrometer utilizing H ₃O ⁺·(H ₂O) _n cluster ions is described. Experiments involving the Cl-atom initiated oxidation of organic species (cyclohexane, cyclopentane, ethane, methane) were performed in the flow reactor and detection of the peroxyl radicals and other oxidation products are discussed. The detection sensitivities for the RO ₂ radicals (R = cyclohexyl, ethyl, and methyl) were estimated. The sensitivities are consistent with a fast rate (coefficient ∼10 ^-9 cm ³ molecule ^-1 s ^-1) for the proton transfer reaction between many RO ₂ species and water-proton clusters. The effect of the presence of water vapor in the ion drift region (IDR) on the detection sensitivity for RO ₂ was investigated. The detection of the methyl and ethyl peroxy radical species was adversely affected by water vapor however, that for the cylcohexyl peroxy radical was much less affected. The cyclohexyl- and cyclopentyl-peroxy radicals were reacted with NO and the products so formed were probed with proton transfer from water molecules. Products identified include a wide array of mono-, di-, and tri-functional species containing peroxyl, alcoholic, carbonyl, nitrate, and peroxynitrate functional groups. These products are shown to be in accord with the current state of knowledge on the oxidation of cyclopentane and cyclohexane.