Mid- and near-IR electronic absorption spectrum of CoO isolated in solid neon. Vibronic data for low-lying electronic states

The optical absorption spectrum of cobalt monoxide generated by reaction of cobalt atoms and oxygen molecules in solid neon at 4 K has been reinvestigated. New data relative to four low-lying electronic states at 0.42, 0.73, 0.87, and 1.26 eV have been obtained in the mid- to near-IR region, each displaying vibronic structure. If assignment of the second low-lying electronic state to A(4)Pi(7/2) can be made clearly following previous gas-phase results, assignments of the first, third, and fourth electronic states to B(4)Sigma, a(6)Delta and b(2)Delta are tentative and suggested in comparison with existing quantum chemical calculations. For all states vibrational frequencies have been measured and an empirical correlation between CoO bond force constant and internuclear distance, using Herschbach and Laurie's relationship, is proposed.