Studies of the reactions of hydrogen atoms by time-resolved e.s.r. spectroscopy

Abstract

Time-resolved e.s.r. spectroscopy has been used to follow directly the reactions of H atoms produced by pulse radiolysis of acid solutions. Detailed analysis of the time profile of the e.s.r. signal was carried out by means of modified Bloch equations. The increased signal found when a scavenger for OH such as t-butyl alcohol is present is shown to be mainly the result of slower H atom decay by radical–radical reaction. The reaction H + OH does not appear to produce any signal polarization. The decay curves observed in the presence of solute are readily accounted for by the treatment, and good plots of pseudo first-order rate constant against solute concentration are obtained. The absolute rate constants for reaction with H atoms are for methanol 2.5 × 10⁶, for ethanol 2.1 × 10⁷, for isopropanol 6.8 × 10⁷, and for succinic acid 3.0 × 10⁶ dm³ mol^–1 s^–1. These values are in good agreement with earlier chemical measurements.