Elementary Reactions J Methods and Systems J Molecular Beams J RadicalsH and 0 atoms and methyl radicals produced in microwave discharges of H2/He, Oz/He and CH4/He mixtures, respectively, were scavenged by supersonic nozzle probing with subsequent freezing and reaction with dimethyl disullide on a liquid nitrogen cooled wall. The main reaction products for the three kinds of radicals were CH3SH, CH3S(0)SCH3 and CH3SCH3, respectively. Side products were CH3SCH2SSCH3 and CH3SSSCH3 for H atoms and CH3S(0)?SCH3 for 0 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.

The method of detecting radicals from low‐pressure gas‐phase systems by scavenging with dimethyl disulfide (DMD) has been applied to microwave discharges in C2H2/He mixtures and to a C2H2/O2 flame. It was accomplished by condensing a supersonic nozzle beam from the reaction system together with a beam of DMD on a liquid‐N2 cooled surface. The scavenging products were measured by GC/MS after warming‐up. Radicals measured in the discharge were C2H, C4H, C6H, C3H2, C2 besides H atoms. Preliminary measurements on the flame showed that C6H5 (phenyl), CH2, C3H2, besides H and O atoms were prominent radicals at the end of the oxidation zone. The concentration of phenyl is of the same order as that of e.g. naphthalene. The method provides a means to distinguish condensible flame products from those that are formed during the sampling process when no scavenger is added.