Observation of Isotope Effects in Sonoluminescence

The spectrum of sonoluminescence emitted by single bubbles of H₂, D₂, He³, and He⁴ trapped in H₂O and D₂O has been measured. We find that heavy water has a dramatic effect on the spectrum of hydrogenic gases, yielding a blackbody-type spectrum with a spectral peak at about 400 nm. The explanation of why such a small change in the driving fluid leads to such a large spectral shift is unknown.