Effects of rare gases on sonoluminescence spectrum of the K atom.

Multibubble-sonoluminescence spectra from Ar-saturated KCl aqueous solutions were measured in the temperature range of 15-40 °C at frequencies of 48 kHz, 148 kHz, and 1 MHz. The effects of dissolved rare gases and the ultrasonic frequency on the shape of the K atom emission spectrum were examined. The line width of the K doublet was independent of the solution temperature, whereas the K line intensity decreased with increasing temperature. The spectra from Xe- and Ar-saturated solutions at 148 kHz exhibited a red-shifted and asymmetrically broadened doublet of K lines. The spectrum from a He-saturated solution, on the other hand, exhibited symmetrically broadened K lines, which were slightly blue-shifted. The observed effects of rare gases are in good agreement with those obtained by gas-phase spectroscopy. These results strongly indicate that the excited K atoms are perturbed by rare gases inside bubbles. The spectra from Xe- and Ar-saturated solutions also indicated that the K doublet is composed of two types of peaks, shifted broadened lines and unshifted narrow lines. These two types of peaks were clearly separated at a frequency of 48 kHz with a high acoustic power in the case of Ar-saturated solutions. The intensity of the broadened lines relative to that of the narrow lines markedly decreased at 1 MHz. Although the narrow lines as well as the broadened lines may have originated from inside the bubbles, the exact mechanism is still unclear.