The rotationally resolved fluorescence excitation spectrum of 1-fluoronaphthalene

A rotationally resolved fluorescence excitation spectrum of the 000 band in the A 1A′←X 1A′ (S1←S0) transition of 1-fluoronaphthalene, at ∼3138 Å, has been observed using a newly constructed laser spectrometer operating in the ultraviolet. The band in question is a hybrid band exhibiting 75% a-type and 25% b-type character, and consists of ∼4000 lines at a rotational temperature of 9 K, each with a FWHM=3 MHz, all of which have been assigned. The band origin is at 31 866.508±0.002 cm−1 (vac), and the rotational constants are A″=1920.6, B″=1122.2, C″=708.5, A′=1891.5, B′=1102.1, and C′=696.6±0.1 MHz. The S1←S0 optical transition moment is rotated away from the a inertial axis by an angle of ±30°, an effect that could have dynamic consequences. Some operating characteristics of the spectrometer are described.