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

Abstract

The reactions Ba + a,-I Baa + a and Ba + CO 2-> Baa + CO have been investigated using the method of laser-induced fluorescence to detect the Baa products. Excitation spectra of Baa produced under single-collision conditions in these reactions are reported, and initial rotational population distributions for Baa formed in the v =0 vibrational level are deduced. The Baa excitation spectrum from the reaction Ba + CO, shows clear band heads and rotationally resolved features which can all be assigned. By contrast, the Ba + a, excitation spectrum is markedly more complex since the band heads are missing and many high (v, J) levels are populated. The Baa 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 + CO, reaction, the dissociation energy of Baa has been determined to be D 8 (Baa) = 133.5 ± 1.3 kcal/mole. Since molecular beam investigations have shown that the Ba + a, 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.

Cluster isolated chemical reactions: Reactivity of Ba atoms and small Ba clusters with SF6 and CO2 molecules on large argon clusters

“…As in the SF 6 case, reaction of barium with CO 2 has been observed in the gas phase: 38 39 This result, obtained by measuring the angular and velocity distribution of the BaO product has been confirmed in a laser induced fluorescence experiment where the measured state analysis of BaO has been remarkably well accounted by phase space calculations. 38 Again, the long-lived reaction intermediate is believed to go through a charge transfer complex Ba ϩ ϪCO 2 Ϫ , and the harpoon model developed in the previous section for the Ba/SF 6 system is expected to also be partly valid to account for the present observation on the Ba/CO 2 system.…”

“…38 Again, the long-lived reaction intermediate is believed to go through a charge transfer complex Ba ϩ ϪCO 2 Ϫ , and the harpoon model developed in the previous section for the Ba/SF 6 system is expected to also be partly valid to account for the present observation on the Ba/CO 2 system. However, CO 2 has a negative electron affinity of Ϫ0.6 eV.…”

The standard molar enthalpies of formation of BaO(g) and SrO(g)

“…As we failed to recalculate the measurements of Jonah et al, (26) Herm et al, (27) and Engelke et al, (28) their results are not given much weight in this assessment. Dagdigian et al (29) used a laser-induced fluorescention reaction. The results from this study are just as the crossed-beam reactions more negative than those obtained with other methods and could not be recalculated.…”

Classical trajectory studies of alkali atom-alkali dimer exchange reactions : Na+Li2and Li+Na2

“…The fraction of energy going into internal modes for these reactions is roughly independent of the total initial energy or its partitioning in the reagents. For the systems studied in the molecular beams experiment [1], it is estimated that ~ 80 per cent of the total available energy goes into product internal modes, which is to be compared with the trajectory value of 60-70 per cent for the reaction Li+ Na e. The statistical expressions for the product energy distributions [26][27][28] are found to be in excellent agreement at low energies with the results from the trajectory analysis. This is particularly so for the translational energy distributions for the exoergic reaction Li+Na e where the distributions have such a distinctive shape.…”

“…At the low collisional energies, the long lifetime of the collision complex allows its decay to be treated statistically with only the constraints of total energy and angular momentum conservation. Approximate formulae have been obtained [26][27][28] for the case of a long-range -C/R 6 potential and large collisional angular momentum. The product energy distributions for a loose three-body complex are given by the form…”