Knowledge Bank

Visible chemiluminescent reactions between Ba(g) and $N2O,NO2,O3$ or $ClO2$ were studied. This selection of triatomic oxygen donors produced a systematic variation of reaction exothermicity, reactant spin states, and electron affinities. Absolute photon yields were measured at room temperature and metal-rich conditions at pressures of 2-250 mtorr. All exhibited a positive pressure dependence, implying the occurrence of collision-induced intersystem energy transfer events via perturbed rovibronic levels. Since the pressure regime studied essentially spans the transition between single- and multiple-collision conditions, efforts were made to identify the nascent (directly-produced) and secondary (transfer-produced) radiating and non-radiating(``dark’’ precursors) excited BaO products from each reaction by comparing pressure-dependent vibronic distributions with existing spectroscopic perturbation information. Each chemiluminescent diffusion flame, because of the nature of the oxidant, generates a different combination of nascent states of Bao, and/or $a3\Pi$. The results and their consequences will be highlighted.