Practice of Kinetics (Comprehensive Chemical Kinetics, Volume 1)

3 MASS SPECTROMETRY 303Gas samplingsystemIonsourceCapacity 1pickupI analyzer [Fig. 8. Block diagram of mass spectrometer employing a chopped beam technique.investigation of metastable, electronically excited oxygen molecules, Oz('A,), asdescribed earlier9*.Molecular beam formation from flames at 1 atmosphere has been discussed.Greene et aI.'ozs lo' used several slits together with differential pumping betweenthe stages. Typical dimensions of the apertures and pressures used by these workersare given in Table 1: the apparatus to which they refer is shown in Fig. 9.Schiff and his colleagues have used, inter alia, mass spectrometric methods tostudy atom reactions in discharge flow systems: reactions of atomic oxygeng9~"',nitrogen'. '6 log and hydrogen7 have been investigated so far by Schiffs group.The basic apparatus used is described in detail in ref. 109. A sampling leak, consistingof a 20 x 20 p cylindrical hole in a pyrex thimble, was fixed in a positionrelatively far downstream in the flow tube. One reactant, usually atoms diluted bytheir molecular precursor, flowed down this tube, and the second reactant couldbe admitted to the flow tube through an inlet jet whose position in the main tubewas adjustable. Since distance in a flow experimknt corresponds to time of reaction,the mass spectrometer leak samples the reaction mixture at various reaction times,and rates of atom reactions can be calculated from the experimental data. Theapparatus has been used to study the reactions N+03, N+NO, 0+03, O+NOZ'O9, H+NOz, H+037, O+02+Oz117, together with investigations of theReferences pp. 336-342