Chemiluminescent reactions of electronically excited alkaline-earth atoms. I. Energy dependence in Ba(6s6p1P1)+CO2→BaO(A,A′)+CO

The visible chemiluminescence from the reaction between a barium atom excited in the 6s6p1P1 resonance state and a CO2 molecule has been studied as a function of the collision energy. The emission originates from a BaO molecule excited in the A 1∑+ and A′ 1Π levels. The population ratio of the electronic A and A′ states appears to be statistical. The internal energy of the electronically excited BaO product is also statistically distributed at low collision energy (0.12 eV) and starts to deviate from statistics when the collision energy is increased, the mean internal energy of BaO remaining almost constant. The cross sections for chemiluminescence are of the order of a few Å2 and depend only weakly of the collision energy. The reaction of Ba (1P) with CO2 to form BaO (A or A′) is interpreted as a direct reaction without a barrier.