RATE MEASUREMENTS BY THE PULSED-ACCELERATED-FLOW METHOD

A pulsed-accelerated-now spectrophotometer with UV-visible capability is described that permits measurement of pseudo-first-order rate const ants as large as 500 000 s(-1) (t(1/2) = 1.4 mu s). Chemical rate proc esses are resolved from physical mixing rate processes by variation of now velocities under conditions of turbulent now, Two mixing processe s are found in the mixing/observation tube, One mixing rate constant, valid for the full length of the tube, is directly proportional to the now velocity, The other mixing behavior, proportional to the square o f the now velocity, is found only in the immediate vicinity of the 10 inlet reactant streams that collide with one another in the middle of the observation tube, Contributions from the latter mixing become more important for very fast reactions that take place close to the inlet jets, These miring models and improved signal/noise permit the measure ment of rate constants for very fast reactions, Applications of the PA F method to electron-transfer, proton-transfer, hydrolysis, and non-me tal redox reactions are reported for pseudo-first-order and second-ord er reactions.