Searching for an isotope effect in sonoluminescence

The only pure liquids in which sonoluminescence from a single stable bubble has been observed are water and heavy water. With regard to the content of the trapped bubble there are a number of gases which yield light. Helium is particularly interesting because its spectrum is strongly peaked in the far ultraviolet. In order to learn about the mechanism responsible for sonoluminescence, the search is on for differences between the spectra of He4 and He3 bubbles in water and heavy water. Other isotope pairs to be compared include hydrogen and deuterium. [Research supported by the U.S. DOE Division of Advanced Energy Projects.]