The effect of fluorocarbon gases on sonoluminescence: a failure of the electrical hypothes is

Ultrasonic irradiation of solutions containing volatile organometallic complexes results in intense emission from excited-state metal atoms. We have determined the effect of dissolved gases (Xe, Kr, Ar, Ne, He, CF4, C2F6, CO, N2) on the intensity of the sonoluminescence resulting from ultrasonic irradiation of silicone oil solutions of Cr(CO)6. This provides a well-defined, spectrally resolved probe of sonoluminescence with emission resulting from a single species, the chromium atom excited states. As predicted by the hot-spot, thermal mechanisms of sonoluminescence, the intensity of excited-state Cr emission decreases with increasing thermal conductivity of the noble gases. The intensity of sonoluminescence increases with increasing ~ (i.e. Cp/Cv), which is also in accord with a thermal mechanism. Sonoluminescence is substantially diminished by the addition of even small amounts (,~ 1%) of CF4 or C2F6, even though they are capable of supporting electrical discharge. This is in agreement with a thermal mechanism, but is in direct conflict with electrical theories of sonoluminescence.