Primary ionic species of α-methylstyrene produced by high energy radiation—A pulse radiolysis study

Abstract

α-Methylstyrene has been irradiated at room temperature in dichloroethane or tetrahydrofuran solution and in bulk with 15 MeV electrons (pulse duration: 30 psec-1 μsec). In dichloroethane, transient absorptions with maxima at 465 and 680 nm were found. The 465 nm peak was assigned to the associated dimer radical cation (M)2+ which is converted effectively to another dimer structure. The latter also has an absorption maximum at 465 nm. The lifetime of (M)2+ is 90 ± 10 nsec. Since the absorption of (M)2+ was observed even after a 30 psec pulse, it was concluded that (M)2+ is formed by the reaction of solvent radical cations ·S+ with associated monomer molecules (·S+ + (M)2 → S + (M)2+). Ethanol and THF were found to react with ·S+, (M)2+ and M.+ (k(M)2+ + EtOH = (8.5 ± 1.0) × 107M−1 sec−1, k(M).+ + EtOH = (3.5 ± 0.7) × 107M−1 sec−1). In THF solutions, the absorption of the radical anion M.- was observed (absorption maximum at 390 nm). Irradiation of bulk α-methylstyrene yielded a spectrum exhibiting the absorption of the different dimer structures. Absorption due to M.+ was not detected. The transformation of the dimer modes was also observed (τ12 = 90 nsec).