PARTICIPATION OF $BaO^{*}_{2}$ IN CHEMLUMINESCENCE OF LOW-PRESSURE Ba(g) + $O_{2}$ FLAMES

$^{1}$.R. Obenauf, C. Hsu, and H. Palmer, Chem. Phys. Lett. 17, 455 (1972). $^{2}$.S. Edelstein, B. Perry, D. Eckstrom, and T. Gallagher, Chem. Phys. Lett. 49, 293 (1977). Research was supported by the National Science Foundation and the Army Research Office.Author Institution:The reaction between Ba(g)and $O_{2}$ generates visible chemiluminescence, $BaO (A^{1}\Sigma^{+} - X^{1}\Sigma^{+})$, even though the exothermicity of the initial bimolecular atom-exchange reaction is less than that Required to directly populate the $A^{1}\Sigma^{+}$ state. Proposed $BaO^{*}$ production mechanism generally contain various sets of secondary reactions involving polyatomic species; a common factor in all sequences has been the incorporation of $BaO^{*}_{2} [1,2]$. New results support the essential correctness of $BaO^{*}_{2}$ as precursor to $BaO^{*}$. The faint orange/yellow glow produced by low-pressure (2 mtorr) $Ba + O_{2}$ flames [1] was enhanced by the addition of $O_{2}$ diluent to the reactor. The broad-band, low-resolutions spectrum of the weak emission from the short-lived flame [1] of Ba burning in pure $O_{2}$ at ca. 10 mttor resembles that obtained by Edelstein, et al. [2], which they tentatively assign to $BaO^{*}_{2}$. Additional confirmation of the existence of a nascent polyatomic comes from the near-thermal appearance of the BaO (A) vibrational distribution in $Ba + O_{2} + $Ar flames at 100 mtorr. Boltzmann character at this low pressure implies that BaO (A) was formed via a long-lived complex