Ion recombination in γ-irradiated naphthalene solutions

Abstract

Ultra-violet absorption spectroscopy shows that C₁₀H⁺₈, (C₁₀H₈)⁺₂, C₁₀H^–₈ and C₁₀H₉ are produced when solutions of naphthalene in hydrocarbon glasses at 77°K are irradiated with γ-rays. Thermoluminescence is produced on warming and is correlated with the presence of ions. The reaction between C₁₀H⁺₈ and C₁₀H^–₈ gives monomer emission only, not excimer emission : therefore, electron transfer must take place before the ions come into contact; excimers are formed from the dimer cations. Addition of electron scavengers (SF₆, CO₂, O₂,N₂O, NO) partially quenches the emission and alters the fluorescence/phosphorescence ratio : N₂ and CF₄ have no effect. “Glow curves” are interpreted in terms of the distribution of ion separations : ion pairs trapped close together recombine first : luminescence in the later part of the glow curves is due to ion pairs with greater separations and these are more likely to be affected by scavengers.