Abstract
The S1(1B1) ← S0(1A1) transition in pyrazine has been investigated. High resolution laser induced fluorescence spectra were obtained by crossing a well collimated molecular beam with UV radiation of an intra-cavity frequency doubled ring laser. The extreme resolution enabled us to observe the molecular eigenstates of the electronically excited state. Most of the spectral features of the S1 state could be interpreted in terms of a slightly perturbed axis switched rotor spectrum. The perturbations show up both in the energy levels of the S1 and in the intensities of the observed transitions.