Multibubble sonoluminescence spectra were measured in sodium dodecyl sulfate (SDS) solutions at the frequencies of 108 kHz and 1.0 MHz. At 108 kHz under a low power, the total sonoluminescence intensity is enhanced and reaches a maximum at l mM. At 108 kHz under a high power, the sonoluminescence intensity gradually decreases in the SDS concentration range of 0.1-100mM, whereas at 1.0MHz, the sonoluminescence intensity is rapidly quenched at a concentration of 1 mM and increases afterward. Na D-line peaks at 589 nm were observed at both frequencies for concentrations above 0.5 mM. Na atom emission is more prominent at 1.0 MHz than at 108 kHz. The frequency effect is discussed in terms of rectified diffusion including dynamic equilibrium isotherm for the surface excess of surfactant and the production of OH radicals.
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