Vapour phase electronic absorption spectrum of nitrosobenzene in the 750 nm region

The vapour phase absorption spectrum of nitrosobenzene has been studied in the 750 nm region. Prominent features of the vibrational structure are sets of four bands separated by approximately 40 cm–1 which can be assigned to the torsional transitions (0′â†� 1″), (0′â†� 0″), (1′â†� 0″), and (2′â†� 0″) around the C—N bond. The spacing of the torsional levels in the first excited singlet state is consistent with a V2 barrier of about 350 cm–1. This represents a sharp reduction from the estimated ground state values of 1300 cm–1. The complete vibrational analysis showed that there is only one electronic absorption system in the 750 nm region and that the complexity of the spectrum is essentially due to the low lying torsional modes.