Practice of Kinetics (Comprehensive Chemical Kinetics, Volume 1)

3 APPARATUS 51-TlmeFig. 39. Variation of radical concentration under quasi-stationary state conditions in the singlepulse-trainmethod. From ref. 133b.of the life-time of the intermediates. The theory may be developed from here toobtain a value for these life-times'.A very similar technique is that of pulsed illumination' 3b, which correspondsvery closely to flash photolysis except that the intensities of the flashes are lo-*times those in the latter technique. The method has been used to determine therate coefficients for reactions (14) and (15).Me. +Me. + CZH,Me- + AcMe -, CH, + AcCH,.A block diagram of the lamp circuit is shown in Fig. 38. Each pulse produced10-5-10-6 % decomposition. They were fired at the rate of 30-40 pulses per second,sufficient to produce a quasi-stationary state. The radical concentration followingeach pulse falls to the same value [R],, prior to the pulse (Fig. 39). A considerationof the rate of formation of CzH6 and CH, leads to an expression from which k,,and k,, may be determined by varying the length of the dark period t'. Pairedpulses with a varying t' should lead to direct evidence for the participation of hotradical reactions.(b) Vacuum ultra-violetThe 1849A resonance line from the low-pressure mercury lamp has already beenreferred to (p. 41). Suprasil'orsapphire windowsallowthe transmissionof thisline1I6or alternatively the lamp may be placed inside the RV13,. The intensity of thet For a detailed discussion see ref. 133a, p. 1113.References pp. 104-1 I I