Practice of Kinetics (Comprehensive Chemical Kinetics, Volume 1)

90 EXPERIMENTAL METHODS FOR SLOW REACTIONSatoms by the vacuum uv line absorption of their resonance lines. Metastable states of0 and N have also been detected. Increasing emphasis is being placed on directIR absorption measurements. Cashion and Polanyi2” have measured the formationof vibrationally excited HCI in the H+C1, and HfHC1 followed by H+CI+Mreactions. Ketene and acetaldehyde have been detected this way in the pyrolysis ofethylene oxide291. The heat of dissociation of Nz04 has been determined frommeasurements of the temperature dependence of the integrated absorption of NO,and N,O, vibration-rotation bandszg2. Using long path cells, elusive intermediateslike CH, NO293 and NO,294 have been identified and estimated. In the latter case,it has been shown that the NO,, produced from 0, +NO Z NO, is the unsym-0metrical OONO rather than O-N(o.IR spectroscopy appears to be a very promising tool for oxidation studies. The rateof formation of carbon monoxide, carbon dioxide and formic acid and the disappearanceof ozone was measured this way with the O,/O, + CH, systemzg5.The system used by Burt and Mink~ff,’~ for the combustion studies is shown inFig. 61. Light from a Nernst filament is split in two and passed alternately throughtwo heated cells F, and F, containing either fuel + N, or fuel + 0,. The beams arerejoined and fed into a Wadsworth monochromator containing a CaF, prism andfinally focussed onto a thermopile, from which a particular signal may be amplifiedand recorded.All these measurements for product analysis are limited by peak overlap, thepossible presence of unknown compounds and the magnitude of the molar extinctioncoefficients, particularly in the infra-red. Here, careful calibrations haveto be made as a function of pressure, using say N, as the di1uent2’”.M4+?:-:-:-;-__--Fig. 61. In situ IR studies of combustion. From ref. 296.