The reactions Ba plus; O2rarr; BaO plus; O and Ba plus; CO2rarr; BaO plus; CO have been investigated using the method of laserhyphen;induced fluorescence to detect the BaO products. Excitation spectra of BaO produced under singlehyphen;collision conditions in these reactions are reported, and initial rotational population distributions for BaO formed in thevequals;0 vibrational level are deduced. The BaO excitation spectrum from the reaction Ba plus; CO2shows clear band heads and rotationally resolved features which can all be assigned. By contrast, the Ba plus; O2excitation 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 (vequals; 0,J) levels populated in the Ba plus; CO2reaction, the dissociation energy of BaO has been determined to beD00thinsp;lpar;BaOrpar;equals;133.5plusmn; 1.3thinsp;kcalsol;mole. Since molecular beam investigations have shown that the Ba plus; O2reaction proceeds through a longhyphen;lived collision complex, the experimentalvequals; 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 fourhyphen;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 longhyphen;lived collision complex.
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