Chemically Inverted Populations and Perturbations Due to Light-Scattering , in Multibubble Sonoluminescence
T.Lepoint, F.Lepoint-Mullie, S.Labouret (Laboratoire de Sonochimie et d'Etude de la Cavitation, Institut Meurice, Brussels, Belgium); C.Petrier (Laboratoire de Chimie Moleculaire et Environnement, Universite de Savoie, Le Bourget-du-Lac, France)
In a first part we describe recent spectroscopic results related to the UV-visible emission from alkali metal - rare gas (M-Rg) and OH(D)-Rg excimers in aqueous and organic multibubble sonoluminescence (MBSL). Three points are analysed: (a) the detection of excimers in MBSL emphazises a singular property of bubbles, namely to break strong molecular bonds (e.g., D0 H-OH = 498 kJmol-1) and to generate fragile van der Waals (vdW) species (D0 Ar-OH* = 8.8 kJmol-1). This implies that the formation and emission from these fragile species is delayed with respect to maximum collapse of bubbles. (b) We show that electronically excited states are populated via third-body chemical reactions. (c) Since the ground states are dissociative in the case of vdW species such as OH(D)-Rg, MBSL causes electronic populations to be chemically inverted. The second part concerns investigations of possible perturbations in the MBSL transmission. This perturbations can be caused by the presence of submicrometric bubbles or solid nanoparticles. Amongst the results we will focus on spectra associated with H2SO4/Rb2SO4 1M solutions containing Al2O3 nanoparticles. The presence of Al2O3 induces a narrowing of Rb lines which reaches up to 20%. We discussed this result in term of weak localisation of light and cooperative effects.
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