Emission from electronically excited metal atoms during single-bubble sonoluminescence

Variations in sonoluminescence (SL) from an acoustically driven but rapidly translating bubble in solutions of sulfuric acid with alkali-metal salts coincide with variations in translational bubble dynamics. At low acoustic pressures, emission from Ar excited states is observed and the bubble motion is smooth and elliptical. At elevated acoustic pressures, SL intensity decreases, emission from excited alkali-metal atoms is observed, and the bubble motion becomes increasingly erratic with frequent and abrupt changes in direction. These results provide a direct experimental link between single and multibubble SL and point toward the origins of sonochemical reactivity of nonvolatile species.