A Rotationally Resolved Fluorescence Excitation Spectrum of all-trans -1,4-Diphenyl-1,3-butadiene

Band 1 in the jet-cooled one-photon S(1) <-- S(0) fluorescence excitation spectrum of all-trans-1,4-diphenyl-1,3-butadiene has been rotationally resolved with a molecular beam laser spectrometer. Both the orientation of the optical transition moment and the rotational constants of the two vibronic levels have been measured. The molecule shows no evidence of being significantly distorted from a C(24) geometry when it is low in the vibrational manifolds of either of the two electronic states.