SONOLUMINESCENCE FROM ALKALI-METAL SALT-SOLUTIONS

Sonoluminescence spectra from alkali-metal salt solutions in water and in primary alcohols are characterized by unusually broad resonance line emission from excited-state alkali-metal atoms. The spectral width and positions of sonoluminescence from potassium in primary alcohols are independent of both solvent vapor pressure and inert gas (Ar/He) ratio. Since the intensity of cavitational heating is dependent on both of these parameters, alkali-metal sonoluminescence cannot be used to determine the local conditions created by acoustic cavitation, contrary to earlier reports. In contrast, the intensity of this sonoluminescence is highly dependent on these two factors. This apparent paradox is explained if the excited-state alkali-metal atoms are the result of secondary reactions of metal ions with high-energy radicals formed directly in the cavitation event. The large line width is caused by rapid collisional deactivation of the excited-state atoms.