Composition and its evolution inside a sonoluminescing bubble by line spectra.

The line emissions of OH*, Na, Na-Ar*, and Ar are observed in stable and bright single bubble sonoluminescence (SBSL), which shows that the composition of the bubble consists of at least three parts: the vapor, droplets of the host liquid, and the gas dissolved in the host liquid. The observation of line emissions in SBSL demonstrates that it shares exactly the same spectra with multibubble sonoluminescences (MBSL). The experiments indicate that noble gas plays an important role in all line emissions of both SBSL and MBSL. The time resolved spectra of SBSL show that there is significant mass exchange between the inside and outside of the bubble. The time scale of the mass exchange ranges from less than 1/10 s to tens of seconds. The SBSL in sulfuric acid supports the argon rectification theory. Because stable SBSL in sulfuric acid can just be achieved within a narrow parameter range, only weak rectification is observed in our experiments.