The Electronic Spectrum of Gaseous CoO in the Visible Region

Abstract

Laser excitation spectra of gaseous CoO have been recorded using Doppler-limited intracavity spectroscopy and supersonic jet-cooled molecular beam methods. As seen in the molecular beam spectra there are nearly 100 bands arising from theX4Δ7/2spin component of the ground state in the wavelength region 430–720 nm. All of them are very strongly red-degraded and most of them are perturbed.59Co hyperfine broadenings or splittings have been observed in many. The bands can be arranged into five electronic transitions, together with a considerable number of “extra” bands induced by perturbations; two of the excited electronic states are4Φ, while the other three, which lie within 1700 cm−1, are4Δ. Semi-empirical calculations have been carried out for the4Δ excited states, using exchange integrals transferred from the TiO and VO spectra; the predicted energies, spin–orbit structures, and relative intensities in absorption are consistent with the assignment of all three4Δ states to the same electron configuration, (4sσ)1(3dδ)3(3dπ)2(3dσ)1. It seems that there are extensive interactions between the excited4Δ states, because only one of them gives rise to a recognizable, though irregular, long vibrational progression in absorption. The other two progressions die out abruptly and unexpectedly after three or four members, presumably as a result of interference effects; however, wavelength-resolved fluorescence studies, together with calculations of the Franck–Condon overlap integrals to the various vibrational levels of the ground state, show that the upper state progressions reappear following a region of confused absorption. All of the excited states show highly irregular variations of their vibrational intervals and rotational constants with the vibrational quantum number,v. The wavelength-resolved fluorescence spectra give evidence for new low-lying electronic states of CoO at 3038, 5989, and 9105 cm−1; based on its vibrational frequency the 3038 cm−1state is possibly the σδ4π2B4Σ−state.