Does water vapor prevent upscaling sonoluminescence?

Experimental results for single-bubble sonoluminescence of air bubbles at v ery low frequency f = 7.1 kHz are presented: In contrast to the predictions of a recent model [S. Hilgenfeldt and D. Lohse, Phys. Rev. Lett. 82, 1036 (1999)], the bubbles are only as bright (10(4)-10(5) photons per pulse) and the pulses as long (approximate to 150 ps) as at f = 20 kHz. We can theore tically account for this effect by incorporating water vapor into the model : During the rapid bubble collapse a large amount of water vapor is trapped inside the bubble, resulting in an increased heat capacity and hence lower temperatures, i.e., hindering upscaling. At this low frequency water vapor also dominates the light emission process.