Practice of Kinetics (Comprehensive Chemical Kinetics, Volume 1)

94 EXPERIMENTAL METHODS FOR SLOW REACTIONSFurnace-Leads- PyrexHeating ~elementTo pumpGasket- TO pump- spectrometerFig. 66. Lossingls RV and ion source. From ref. 310.was sampled through a gold leaf diaphragm D, the remaining gases being pumpedout at PI through the annular space between Q and the water jacket W. (Thechances of catalysed combination of free radicals at D is very high.) This methodtends to be unreliable since the ionisation efficiency is low and varies with the electronenergy. An alternative which, in many cases, allows quantitative measurementsto be made, has been developed by Lossing et ~1.~~'. The net peak height andhence the concentration of the radical may be determined provided that all thereaction products that contribute to a radical peak are identified. The apparatusused by these authors is shown in Fig. 66. The sample leak consists of a quartzthimble, through the thin top of which a pinhole is produced by a Tesla discharge.