Gas-phase absorption spectrum of triplet naphthalene in the 220-300-nm and 410-620-nm wavelength regions

A recently developed method for kinetic spectroscopy based on modulated excitation of mercury-photosensitized reactions was employed to investigate the gas-phase triplet absorption spectrum of naphthalene in the visible and ground-state absorption regions of the spectrum. At least four distinct electronic transitions were observed and assigned as follows (transition energy in electron volts, symmetry species of upper state, oscillator strength where determined): 2.25, 3Ag+; 2.93, 3Ag-; 4.86-5.06, 3Ag-; 5.46, 3B1g-, f = 0.50. A value of f = 0.14 was found for the well-known 3B1g- transition at 3.12 eV. Extinction coefficients were estimated from the observed ground-state depopulation signal. The spectrum appears to be in essential agreement with the theoretical predictions by de Groot and Hoytink.