Number 246 (Story #3), October 25, 1995 by Phillip F. Schewe and Ben Stein ISOTOPE EFFECTS IN SONOLUMINESCENCE have been observed by Seth Putterman and Robert Hiller at UCLA. Sonoluminescence (SL) is a mysterious phenomenon in which acoustic energy is transduced into light energy; high frequency sound waves are absorbed by tiny bubbles in water. The bubbles, oscillating wildly, re-emit the energy in the form of tiny, focused light bursts. Many things about SL are still unknown, such as the nature of the light-emitting process or why the light pulses are so short. The UCLA work has established one new fact: substituting heavy water (D2O) for ordinary water (H2O) as the liquid medium causes the center of the SL spectrum to dramatically shift from ultraviolet toward red wavelengths. This result seems to represent yet a new mystery. According to the researchers, "The shift is remarkably large, especially in view of the small difference in chemical and elastic properties between light and heavy water." (Robert A. Hiller and Seth Putterman, upcoming article in Physical Review Letters; journalists can obtain copies from AIP Public Information, physnews@aip.org)