The A5Π–X5Π electronic transition of CrO, near 6000 Å, has been analysed in detail using laser-induced fluorescence and conventional discharge emission spectroscopy. The transition provides the first instance where it has been possible to analyse the rotational structures of quintet electronic states completely. Although the parallel polarization of the transition has prevented the spin–orbit coupling and Λ-doubling intervals from being observed directly, it is shown that sufficient indirect information exists in the spectrum for them to be obtained with fair precision. The excited state, A5Π, is perturbed by large numbers of other electronic states which have no intensity of their own for emission to the ground state. The analysis of the perturbed regions has been greatly facilitated by the laser-induced fluorescence spectra: the excitation spectra correspond to a rotational temperature close to room temperature (which offers a significant improvement in resolution over the discharge spectra), and the J-assignments of the perturbed lines given by the resolved fluorescence spectra are unambigious
