Pressure during sonoluminescence

Multibubble sonoluminescence (MBSL) spectra were collected from solutions containing volatile metal-containing compounds in silicone oil saturated with helium or argon. Ultrasonic irradiation of these solutions at 20 kHz and go W/cm(2) led to emission from excited states of the free metal atoms. The widths and peak positions of these lines varied as a function of the gas used to saturate the solution, indicating that the emission was from the gas phase of the bubble. High-resolution MBSL spectra showed that the pressure within the bubble at the point of emission was on the order of 300 bar in argon-saturated silicone oil, which is consistent with simple adiabatic compression during cavitation.