Pulse radiolysis of liquids at high pressures. IV. Hydrogen-atom reactions in aqueous 0.1<i>M</i> HClO4 solutions

Abstract

Absorption spectra were determined for various times after a 10-nsec radiation pulse to 0.1M HClO4 solutions containing AgClO4 with and without tert-butyl alcohol (TBA). The spectra and their time dependence, which show the same features at 1 atm and 6.6 kbar, are interpreted in terms of the following reactions: H + Ag+ → H+ + Ag [2], OH + Ag+ → OH− + Ag2+ [5], Ag + Ag+ → Ag2+ [6]. Scavenging of OH by TBA prevents formation of Ag2+ which has an absorption peak near 270 nm. For solutions containing TBA, a 60-nsec spectrum with a peak at 370 nm is assigned to Ag and a 7-μsec spectrum with a peak at 310 nm and shoulder at 260 nm is assigned to Ag2+. Growth and decay of Ag absorption at 410 nm were studied with solutions containing TBA at 29 °C and six pressures in the range 1 atm–6.7 kbar; the reactions of H with glycerol and ethylene glycol were studied by their competition with Reaction [2] in solutions also containing glycerol or ethylene glycol. The results give atmospheric-pressure specific rates of 2.8 × 1010, 3.8 × 107, and 1.9 × 107M−1·sec−1 and pressure-independent activation volumes of 1.7, − 5.0, and − 4.2 ml mol−1 for the reactions of H with Ag+, glycerol, and ethylene glycol, respectively. Results of this study and a previous γ-radiolysis study are combined to give best values of (1) ΔV‡ = 2 ml mol−1 for the diffusion-controlled reactions of H with Ag+ and O2 and (2) ΔV‡ = − 5 ml mol−1 for each of 15 presently studied reactions of H not controlled by diffusion. From such results it is concluded that (1) diffusion of H is governed in some manner by the viscosity of water and (2) V̄ (H) = 5 ml mol−1 and is incompressible.