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Barium dimers have been produced and stabilized by the successive pickup of two barium atoms on large argon clusters (average size of 8000). By adding chlorine and oxygen molecules, chemiluminescent reactions of these dimers have been observed. This technique of dimer formation can be extended to higher order clusters to study reactions of cold metallic clusters.

Barium atoms at the surface of large argon clusters are excited into the 6s6p1P1 state leading either to ejection and subsequent fluorescence of the free barium atom or to fluorescence of solvated barium. Relative probabilities for these two processes as a function of the excitation energy and of the cluster size are presented. By comparison with the binding energy from a molecular dynamics (MD) calculation, we find that the barium atom is not excited above the limit for direct dissociation. The nonzero desorption probability is attributed to the gain of surface energy of the argon cluster which is partially transferred to the barium atom. Using linearly polarized laser light for the excitation, a positive polarization of the fluorescence of the ejected barium atoms is observed, whereas the polarization fluorescence of the solvated barium is negative. This indicates that the solvated barium atoms undergo a relaxation process which rotates the orientation of the excited orbital before the fluorescence. The...

This work presents a quantitative comparison between experiment and molecular dynamics simulations for the excitation spectra of large van der Waals clusters. The emission and excitation spectra of mixed Ba(Ar)n clusters have been obtained for average cluster sizes ranging between 300 and 4000. The simulation is performed by using classical dynamics and pairwise additive potentials for two cases corresponding to the barium atom at the surface or inside the argon cluster. A very good agreement with the experiment is found when the barium atom is at the surface.

The present paper investigates chemiluminescence in reactions of excited barium atoms (6s6p 1P1) with water and a series of alcohols and ethers. The electronically excited product molecule from the reaction with H2O (and D2O) is BaOH (and BaOD) in the A 2Π, A’ 2Δ, and B 2Σ levels. The product molecule is always Ba–ORx in reactions with alcohols ROH, whatever the size of the alcohol (methanol to butanol), and whatever its class (primary to tertiary). By comparison, no chemiluminescence was observed when the reactant was dimethyl and diallyl ether although allowed energetically. The nature of the product molecules in reaction with alcohols, and the absence of reaction with ethers that were found here are remarkably close to what was found by Davis et al. (submitted to J. Chem. Phys.) for the formation of ground state products in reactions of Ba(6s5d 1D2) with water, methanol, and dimethyl ether. The present work thus allows us to extend the model of Davis et al. for the reactivity of Ba(6s5d 1D2) as a power...

Doppler measurements taken over a range of probe‐laser angles in a crossed‐beam experiment were used, in conjunction with forward convolution analysis, to obtain flux–velocity contour maps for Ba(3P2) produced in a collision of Ba(1P1) with H2, N2, O2, and NO. The contour maps suggest a general model for the dynamics of this process in which large impact parameter collisions result in a near‐resonant transfer of initial electronic energy into final vibrational energy, while close collisions produce sideways scattering and effectively couple electronic energy to translation. The molecular collision partners fall into two categories: for one group, comprising O2 and NO, the existence of a well‐defined molecular anion with favorable Franck–Condon factors linking excited vibrational levels to the ground vibrational state of the neutral results in greatly enhanced coupling for the near‐resonant process. Molecules for which there exist no stable anions, such as N2 and H2, represent a second category. The electronically inelastic collision for this group is instead dominated by the nonresonant process yielding the ground vibrational state and large translational energy release.

The reaction of Ba(6s 6p1P1) with O2 has been investigated in a crossed beam experiment as a function of the collision energy. The electronically excited product BaO is not statistically populated and the difference from statistics increases with the collision energy. Such a result is markedly in contrast with what was observed in the reactions of Ba(6s21S0) and Ba(6s5d1D2) with O2 where the existence of a long‐lived complex results in a statistical distribution of internal energy of the BaO product. The present result is interpreted as due to the collisional system following a different channel involving excited electronic states of the intermediate, BaO2 above the ionization limit, instead of the strongly bound states of barium peroxide which are involved in reactions of less excited Ba states.