THE ELECTRONIC-SPECTRUM OF GASEOUS COO IN THE VISIBLE REGION

Laser excitation spectra of gaseous CoO have been recorded using Doppl er-limited intracavity spectroscopy and supersonic jet-cooled molecula r beam methods, As seen in the molecular beam spectra there are nearly 100 bands arising from the X4 Delta(7/2) spin component of the ground state in the wavelength region 430-720 nm. All of them are very stron gly red-degraded and most of them are perturbed, Co-59 hyperfine broad enings or splittings have been observed in many. The bands can be arra nged into five electronic transitions, together with a considerable nu mber of ''extra'' bands induced by perturbations; two of the excited e lectronic states are (4) Phi, while the other three, which lie within 1700 cm(-1) are (4) Delta. Semi-empirical calculations have been carri ed out for the (4) Delta excited states, using exchange integrals tran sferred from the TiO and VO spectra; the predicted energies, spin-orbi t structures, and relative intensities in absorption are consistent wi th the assignment of all three (4) Delta states to the same electron c onfiguration, (4s sigma)(1) (3d delta)(3)(3d pi)(2)(3d sigma)(1) It se ems that there are extensive interactions between the excited (4) Delt a states, because only one of them gives rise to a recognizable, thoug h irregular, long vibrational progression in absorption. The other two progressions die out abruptly and unexpectedly after three or four me mbers, presumably as a result of interference effects; however, wavele ngth-resolved fluorescence studies, together with calculations of the Franck-Condon overlap integrals to the various vibrational levels of t he ground state, show that the upper state progressions reappear follo wing a region of confused absorption. All of the excited states show h ighly irregular variations of their vibrational intervals and rotation al constants with the vibrational quantum number, v. The wavelength-re solved 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(-1) state is possibly the sigma delta(4) pi(2)B (4) Sigma(-) state. (C) 1997 Academic Press.