Scavenging of Radicals from the Gas Phase by Freezing with Dimethyl Disulfide

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Abstract
H and O atoms and methyl radicals produced in microwave discharges of H2/He, O2/He and CH4/He mixtures, respectively, were scavenged by supersonic nozzle probing with subsequent freezing and reaction with dimethyl disulfide on a liquid nitrogen cooled wall. The main reaction products for the three kinds of radicals were CH3SH, CH3S(O)SCH3 and CH3SCH3, respectively. Side products were CH3SCH2SSCH3 and CH3SSSCH3 for H atoms and CH3S(O)2SCH3 for O atoms. – The scavenging efficiencies for the different radicals were determined and measured as a function of the gas phase radical concentration, the flow of scavenger molecules, the pressure in the vacuum chamber, and the conditions of the discharge and the flow through the sampling nozzle. It is concluded that this method is suitable for light radicals with reservations in the case of H atoms and can probably be used with still better success for heavier radicals.