title: Nonequilibrium vibrational excitation of OH radicals generated during multibubble cavitation in water.
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.
authors.affiliation: Institute for Separation Chemistry of Marcoule, UMR 5257-CEA-CNRS-UMII-ENSCM, BP 17171, 30207 Bagnols sur Cèze Cedex, France.
authors.forename: Abdoul Aziz
authors.initials: AA
authors.lastname: Ndiaye
authors.forename: Rachel
authors.initials: R
authors.lastname: Pflieger
authors.forename: Bertrand
authors.initials: B
authors.lastname: Siboulet
authors.forename: John
authors.initials: J
authors.lastname: Molina
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Dufrêche
authors.forename: Sergey I
authors.initials: SI
authors.lastname: Nikitenko