High intensity ultrasound creates localized hot-spots in liquids through the process of cavitation: the formation, growth, and implosive collapse of bubbles. Local heating produces excited states of diatomic carbon (C2) from hydrocarbons; these states emit light just as they do in a flame. The image of such sonoluminescence from a vibrating titanium rod (1 cm diameter) is shown in false-color. The temperature created in cavitation hot-spots, determined from the spectrum of this emission, is ~5000 K. [Photograph by J. A. Gray, K. A. Kemper, and K. S. Suslick in the Department of Chemistry of the University of Illinois at Urbana-Champaign; from work funded by the National Science Foundation.]
Flint, E. B.; Suslick, K. S. "The Temperature of Cavitation," Science 1991, 253, 1397-1399.
