Ionic Processes in γ-Irradiated Organic Solids: Positive-Hole Migration in 3-Methylpentane

Abstract

The yields of positive and negative species trapped in γ-irradiated organic glasses at −196° have been measured as a function of glass composition. Increased yields of solvent-trapped electrons (e−) and biphenyl anions (φ2−), as well as decreased yields of various solute cations (A+), were noted when additives capable of undergoing charge-transfer or proton-transfer reactions were present in small amounts (<2 mole %) in 3-methylpentane (3MP). All results can be understood qualitatively in terms of the mobile positive hole being transferred from 3MP to these additives and trapped. A simple scheme of competition for the total available number of positive holes accounts for the decrease in A+ when a second solute (B) is added and relative cross sections to form A+ and B+ can be determined. Additives affect the optical absorption spectrum of (e−) in 3MP. The spectra of the biphenyl positive and negative ions are similar but displaced, while the anion and cation from benzene are anomalous in 3MP glass. The rates of decay of N,N,N′,N′-tetramethyl-phenylenediamine cation and of (e−) are compared following γ irradiation and photoionization of the amine in 3MP. Very efficient attachment of photoelectrons by φ2 indicates an average track volume >10−18 cc.