Vibrationally excited BaO(X 1Σ+) was produced by reacting Ba atoms with O2 under “jet flow” conditions in which the convective flow velocity was large compared with the diffusion velocities so that the relaxation could be spatially resolved. The vibrational level populations were determined by laser-induced fluorescence measurements. By using modeling calculations to fit the spatial variation of the apparent vibrational temperature, we obtained a vibrational relaxation rate for BaO(X 1Σ+), ν = 1 → ν = 0, by Ar, of 9 × 10−13 cm3/molecule s.

A study of the spatially resolved chemiluminescence of the Ba + O2 reaction suggests that the emission is due to production of the excited states of BaO, Ba2O, and BaO2 formed in three-body recombination reactions.

The magnitudes and distributions of alkali atom emission have been measured for Li+NF3, Na+NF3, Cs+NF3, and Cs+F2 flames. The production of excited states in all cases follows a gi(Eion−Ei)3 dependence, where gi and Ei are the degeneracy and energy of the state, and Eion is the ionization energy of the alkali atom. This suggests that the primary excitation mechanism involves electron–ion recombination. Examination of other data shows that this energy dependence of excitation may hold in a variety of reaction systems and experimental conditions. Measured photon yields for atomic emission ranged from 0.2% to 3%; considerably higher values would be expected in the absence of radiation trapping. There is no evidence for substantial population inversions between any of the atomic states.

Chemiluminescence spectra and photon yields are presented for reactions of Ba, Sm, and Eu with N2O, O3, O2, F2, and NF3 for the pressure range 0.5–20 torr. Peak yields range from 2.5% to 70%, with the reactions of Sm with NF3 and F2 having the highest yields. These latter reactions put from 12% to 16% of their available thermal energy into luminous output. The pressure dependence of the photon yields deduced from these and other recent measurements suggests that the initial exothermic reaction primarily populates high vibrational levels of the ground electronic state of the newly formed diatomic. Radiating states would then be populated mainly by collision‐induced vibrational‐to‐electronic internal conversion.