The UV absorption spectrum of the phenyl radical isolated in solid argon

Abstract

Phenyl radicals have been generated by photodecomposition of nitrosobenzene isolated in solid argon at 12 K. In this medium the origin of the first UV absorption band of nitrosobenzene corresponding to theS ₀ →S ₂ transition is found at 30260 cm⁻¹. Excitation with an excess energy of ≈ 2200 cm⁻¹ results in very efficient photodissociation. The fragments NO and phenyl are stable for many hours. Annealing of the sample above 35 K led to partial recombination and recovery of the absorption spectrum of nitrosobenzene. The UV spectrum of the phenyl radical was obtained in the wavenumber range 25000–45000 cm⁻¹, apparently without contamination by other species. It shows sharp lines at 25220, 33880, and 34820 cm⁻¹ and two broader maxima at 38360 and 41060 cm⁻¹. Of these only the line at 34820 cm⁻¹ had been assigned to the phenyl radical in earlier work. These data are compared to recent molecular orbital calculations.