A microwave temperature-jump apparatus for the study of fast reactions in solution

An apparatus for the determination of the rates of fast chemical reactions in solution is described. The temperature of a solution is raised, by means of a pulse of microwaves, by about 0.4 degK; the resulting shift of chemical equilibrium is followed spectrophotometrically with the help of a short-response photoelectric system and oscilloscope. The light beam passing through the solution must be of high intensity, in order to achieve a satisfactory signal-to-noise ratio, and a photocell is therefore used in preference to a photomultiplier. The photocell is connected directly to an amplifier without an intermediate cathode follower, in order to reduce electrical pick-up. Reactions with half-times down to about 1 μsec can be studied, and rate constants accurate to within about ±10% can be derived. In favourable cases, rate constants up to 10 10 1. mole -1 sec -1 could be determined.