Abstract (Invited) |
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)
e-mail:
tlepoint@meurice.heldb.be
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.
Section
: 11