Formation of the Triplet State of Naphthalene in the Pulse Radiolysis of Gaseous Mixtures of Benzene and Naphthalene

A significant yield of the lowest triplet state of naphthalene is observed when 1.9 atm benzene containing small amounts of naphthalene is pulse irradiated in the gas phase at 120°C. The yield is independent of naphthalene concentration from 0.3 mole % to at least 3 mole %. Electron scavengers (SF₆ and CCl₄) decrease the yield by 70%, as does a positive‐ion scavenger, triethylamine. This 70% is thought to originate by neutralization of C₁₀H₈⁺ by C₁₀H₈⁻. The other 30% of the triplet yield is thought to originate from benzene ${(}^3{B}_{\text{1u}})$ formed directly by the irradiation of the benzene vapor. Naphthalene was found to be 34 ± 4, 38 ± 4, and 18 ± 2 times more efficient in accepting energy from the benzene triplet than trans‐butene‐2, cyclohexene, and nitromethane, respectively. Similar results were obtained using 1.3 atm argon as the main gas, with about 3 mole % benzene and about 3 × 10⁻³ mole % naphthalene present at 25°C. In this case, the naphthalene triplet was formed after the pulse, and kinetic analyses of the curves as a function of naphthalene concentration allowed an evaluation of the benzene ${(}^3{B}_{\text{1u}})$ decay constant of 1.3 × 10⁵ sec⁻¹ at 18 torr benzene (which decreases with increasing benzene pressure) and of the rate constant for energy transfer from benzene ${(}^3{B}_{\text{1u}})$ to naphthalene of (3.0 ± 0.5) × 10¹¹ liter mole⁻¹·sec⁻¹. Naphthalene was found to be 20 ± 3 times more efficient than trans‐butene‐2 in accepting energy from triplet benzene.