Sonochemistry resonance frequency

In contrast to other oxidative processes run under silent conditions, no PTC is necessary. In a two-phase system consisting of aqueous KMn04 and indane in benzene, an 80% yield can be obtained, provided the pressure in the reaction vessel is reduced to ca. 450 torr. This effect is interpreted by a resonance between the ultrasonic frequency and the vibration frequency of the bubbles, the radii of which is a function of the pressure (Ch. 2, p. 54). Optimal energy transfer is ensured under these conditions, and the importance of the pressure parameter, not frequently evidenced in sonochemistry, is illustrated. 

Experiments have shown that aqueous sonochemistry is unchanged over the frequency range in which cavitation occurs i.e. 10 Hz to 10 MHz [22]. Since there is no direct coupling of the sound field with species on a molecular level, changing the frequency of the sound input simply alters the resonant size of the cavitation bubble. The effect of this over the range of interest is negligible. It should, however, be noted that although there is both an upper and a lower limit to the frequencies at which cavitation will occur, the band of frequencies used for sonochemistry lies well within these limits. 

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