Practice of Kinetics (Comprehensive Chemical Kinetics, Volume 1)

50 EXPERIMENTAL METHODS FOR SLOW REACTIONSThe rate of formation of some intermediate in steady illumination (RSJ is givenby equation D‘where A is a proportionality constant, I, is the light absorbed and 0 < IZ < 1.Since r is the ratio of dark to light periods, the fraction of the time that the lightis on is l/(r+l). If at low sector speeds the time between light periods is longcompared with the life-time of the intermediates, the rate of formation of these(Rslow) is the time average of the rate under steady illumination (RSJ and the zerorate for dark periods, i.e.At fast sector speeds, when the flash period is short compared to the life-time ofthe intermediates, the effective light intensity is IJ(r+ 1) and Rfast is given by equation(F’):When n = 112 and r = 3, B = 1/4 and C = 1/2. The transition between these twovalues occurs when the period of time between flashes is of the order of magnitudeFOsctllatorCapacitorCapacitorPowerInitialDelayedPowerSUPPIYFig. 38. Block diagram of the lamp circuit for pulsed illumination studies. From ref. 133b.