Rotationally resolved electronic spectroscopy of 4-aminobenzonitrile

The rotationally resolved fluorescence excitation spectrum of the 000 band in the S1 ← S0 transition of 4-aminobenzonitrile (ABN) was recorded, at 299 nm, by using laser induced fluorescence in a molecular beam apparatus. This spectrum exhibits pure b-type character, which indicates that the electronic transition moment vector is oriented along the short molecular axis. The rotational constants of the S0 and S1 states were determined. In addition, the rotationally resolved fluorescence excitation spectra of two vibronic bands in the S1 state, at 807 and 816 cm−1, were recorded. The molecular structure of the ABN molecule is discussed by comparing the rotational constants and the inertial defects.