THEORETICAL-STUDY OF THE SPECTROSCOPY OF THE ALKALI OXIDES LIO, NAO, AND KO

Theoretical calculations show that only three of the eleven doublet electronic states of LiO, NaO, and KO dissociating to the three lowest asymptotes are significantly bound. The only bound-bound transitions that occur in the visible and infrared spectral regions are from the C 2-PI state to the lowest two ionic states (2-PI and 2-SIGMA+). The emission is dominated by the C 2-PI-X 2-PI transition, which has a very large transition moment near r(e) (C 2-PI). Although chemiluminescence observed for these alkali oxides has been correctly assigned to this transition, the vibrational assignments are incorrect, as the strongest transitions from the lower vibrational levels of the C 2-PI state are into rather high vibrational levels of the X 2-PI state. The radiative lifetimes for the C 2-PI(upsilon = 0) level are 66.2, 90.7, and 315.5 ns for LiO, NaO, and KO, respectively: the C 2-PI-A 2-SIGMA+ channel contributes less than 1% to the radiative lifetimes. Emission spectra are presented for the C 2-PI-X 2-PI band systems of LiO, NaO, and KO. Except for very high vibrational temperatures, most of the emission occurs in the infrared region. The maxima in the spectra shift to longer wave-lengths for the heavier alkali oxides, paralleling the decrease in the T(e)(C 2-PI) values.