Peering into Collapsing Bubbles

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Science  05 Feb 2010:
Vol. 327, Issue 5966, pp. 625
DOI: 10.1126/science.327.5966.625-b

A liquid excited by ultrasonic pressure waves emits a short burst of light caused by the implosion of either single bubbles or clouds of bubbles. Spectroscopy of this sonoluminescence has shown that temperatures of several thousand kelvin may be associated with bubble collapse, but it has not been clear how homogeneous the temperature profile within a cloud of bubbles is. To address this question, Xu et al. have measured the spectroscopic temperature in bubble clouds formed in aqueous phosphoric acid, using molecular emissions from both OH and PO radicals. The results show that there are two different bubble populations in the cloud. One population, associated with OH emission, collapses symmetrically and has a temperature of around 9500 K; the other, associated with PO emission, comes from colder bubbles (∼4000 K) that collapse nonsymmetrically. These properties of collapsing bubbles will affect the course of the local chemistry.

Angew. Chem. Int. Ed. 49, 1079 (2010).

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