THE SONOLUMINESCENCE SPECTRUM OF SEAWATER

The sonoluminescence spectra of seawater and of a sodium chloride solution were determined by irradiation with ultrasound at 20 kHz. Ultrasound creates sonoluminescence through the process of acoustic cavitation: the formation, growth and implosive collapse of bubbles in a liquid. The sonoluminescence spectra of both seawater and NaCl in water are characterized by an emission line at 589 nm from excited-state sodium. Excited-state Na atoms are produced from the reaction of Na+ with high-energy hydroxyl radicals formed directly during the cavitation event. Emission at 589nm could be useful in determining whether sonochemical processes associated with cavitation occur in breaking waves or other turbulent flows.