Arrays of gas bubbles of uniform size are generated in a liquid and subjected to sound at a frequency of 30 kHz. In a viscous mixture of glycerine and water, sonoluminescence is produced in the absence of cavitation noise or streamer activity. Under relatively low amplitude conditions the light occurs in flashes with the same frequency as the sound field, and with duration less than onehyphen;tenth that of the sonic period. The phenomenon is believed to be associated with volume pulsations of the bubbles and, specifically, with dissociation of H2O into the radicals OH and H during the compression phase of each cycle when the temperature is relatively high. Photons are emitted as the radicals recombine. Calculations suggest that about 108photons/sec might be expected from a single 0.2hyphen;mmhyphen;diam bubble by this mechanism when the bubble temperature reaches 1800deg;K. Bremsstrahlung (from accelerated charges) is negligible under these same conditions.
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