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Activating Molecules, Ions, and Solid Particles with Acoustic Cavitation
Published on: April 11, 2014
Nonequilibrium vibrational excitation of OH radicals generated during multibubble cavitation in water
Abdoul Aziz Ndiaye1, Rachel Pflieger, Bertrand Siboulet
1Institute for Separation Chemistry of Marcoule, UMR 5257-CEA-CNRS-UMII-ENSCM, BP 17171, 30207 Bagnols sur Cèze Cedex, France.
Abstract:
The sonoluminescence (SL) spectra of OH(A(2)Σ(+)) excited state produced during the sonolysis of water sparged with argon were measured and analyzed at various ultrasonic frequencies (20, 204, 362, 609, and 1057 kHz) in order to determine the intrabubble conditions created by multibubble cavitation. The relative populations of the OH(A(2)Σ(+)) v' = 1-4 vibrational states as well as the vibronic temperatures (T(v), T(e)) have been calculated after deconvolution of the SL spectra. The results of this study provide evidence for nonequilibrium plasma formation during sonolysis of water in the presence of argon. At low ultrasonic frequency (20 kHz), a weakly excited plasma with Brau vibrational distribution is formed (T(e) ~ 0.7 eV and T(v) ~ 5000 K). By contrast, at high-frequency ultrasound, the plasma inside the collapsing bubbles exhibits Treanor behavior typical for strong vibrational excitation. The T(e) and T(v) values increase with ultrasonic frequency, reaching T(e) ~ 1 eV and T(v) ~ 9800 K at 1057 kHz.
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