Rapid scanning [1, 2] in ESR spectroscopy is one of the methods by which one can obtain significant information relating to rapid chemical reactions occurring in several milliseconds. One of the advantages of this rapid scanning method is the ability to investigate phenomena occurring rapidly and singly, such as a decay of electrons trapped in a solid matrix. This note reports on the coupling of an electronic computer (JEOL JEC-5) with the rapid scan unit in order to record ESR spectra with high signal-to-noise ratio in several milli-seconds, and also on the successful application of this technique to the study of chemical reactions. This use of the computer is neither as a computer of average transients (CAT) [3, 5] nor as a sampling method for the detection and display of rapidly changing spectra [6, 7]. The apparatus used in this experiment consists of an ESR spectrometer, a Helmholtz coil, a power amplifier, a sawtooth wave generator, a trigger pulse generator, and an electronic computer. A block diagram of the equipment is shown in Fig. 1. Although details of the rapid scan method and the units other than the computer were described in a previous paper [2], several parts have been improved as follows. The dimensions of the Helmholtz coil were changed to 10.2 cm outer diameter and 6.5 cm inner diameter, and the unit was made of 10 turns of 0.7-mm copper wire. By feeding the sawtooth current to the coil after amplification by a solid-state SEPP OTL power amplifier a more linear field sweep was obtained than previously.† The trigger pulse, the repetition rate of which ranges from 200 msec to 10 sec, initiates simultaneously both the sawtooth wave generator and the computer. The purpose of using the computer is to store the ESR spectra observed by the rapid scan method during a rapid chemical reaction and to display these spectra on the chart of a conventional recorder after complete termination of the reaction. About 100 μsec are required for analog-to-digital conversion in the computer used. Sixteen ESR spectra, each of which was ob served for 20 msec, were stored in the computer during a chemical reaction. For this operation a program was compiled so as to store 192 sampling points for each spectrum; the number of these sampling points was sufficient to get a precise and smooth curve for each spectrum displayed. The application of the technique was demonstrated for an experiment on the decay reaction of the electrons trapped in 2-methyltetrahydrofuran, MTHF.
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