Product state analysis of BaO from the reactions Ba + CO2 and Ba + O2

Abstract

The reactions Ba + O2 → BaO + O and Ba + CO2 → BaO + CO have been investigated using the method of laser-induced fluorescence to detect the BaO products. Excitation spectra of BaO produced under single-collision conditions in these reactions are reported, and initial rotational population distributions for BaO formed in the v=0 vibrational level are deduced. The BaO excitation spectrum from the reaction Ba + CO2 shows clear band heads and rotationally resolved features which can all be assigned. By contrast, the Ba + O2 excitation spectrum is markedly more complex since the band heads are missing and many high (v, J) levels are populated. The BaO rotational distributions for both reactions are found to be nonthermal, based on comparisons with simulated spectra. Estimates of the initial vibrational populations are also obtained. By extrapolation of the highest observed (v = 0, J) levels populated in the Ba + CO2 reaction, the dissociation energy of BaO has been determined to be D00 (BaO)=133.5± 1.3 kcal/mole. Since molecular beam investigations have shown that the Ba + O2 reaction proceeds through a long-lived collision complex, the experimental v = 0 rotational distributions have been compared with those calculated by phase space theory and transition state theory. The previous treatments of these statistical models have been extended to four-atom complexes. The results of the transition state theory reproduce the qualitative features of the experimental distributions, while the results of the phase space theory are in remarkable agreement with experiment. This strongly suggests that the dynamics of both reactions are governed by the formation of a long-lived collision complex.