Sonochemistry and Sonoluminescence of the N2/Ar/H2O system
Ouerhani T.*, Pflieger R., Nikitenko S. I.
Institut de Chimie Séparative de Marcoule, UMR5257, CEA-CNRS-UM2-ENSCM, Centre
de Marcoule, Bat. 426, BP 17171, 30207 Bagnols-sur-Cèze cedex, France
The multibubble sonoluminescence (MBSL) emission and the sonochemical activity of
N2/Ar/H2O system are measured in order to study their connection.
The MBSL spectra of water sparged with Ar/N2 gas mixtures are systematically studied in a
large range of ultrasonic frequencies (20, 204, 362, 613 and 1057 kHz) using the
multifrequency sonoreactor described recently[1]. At 20 kHz the presence of 10 % N2 in the
sparging gas hardly modifies SL spectra, neither in their intensity nor in their shape. At high
frequency the spectra show the emission of OH(A-X & C-A) systems and another peak around 336
nm on top of the continuum (Fig.1). The emission of N2(C-B) system, comprising three main peaks
at 315, 336 and 357 nm [2] is absent. The intense peak at 336 nm is assigned to NH(A-X)
system. The evolution of its intensity is followed as a function of N2 content in the sparge gas.
The maximum intensity is obtained between 20 and 40% of N2 content in Ar (Fig.2).
Fig1. MBSL spectrum of water sparged with Ar/ 14 % N2 at 359 kHz, Pac=59 W, T=11°C.
On the other hand, the rate of formation of sonolysis products was followed during the
sonolysis of water sparged with various Ar/N2 mixtures: WH2 by mass spectrometry, WH2O2
and WNO2- by absorption spectroscopy and WNO3-by ion chromatography method. The results
show a complex behavior: WH2 and WH2O2 decrease with N2 content in Ar, WNO3- is almost
constant and smaller than WNO2- and WNO2- increases with N2 content in Ar till a maximum
between 40 and 60% of N2 in Ar (Fig.2).
Comparison of the MBSL spectra with spectra from discharge plasma indicates that NH is
formed by N2 dissociation followed by reaction with H2O molecule [3].
Based on the comparison of the MBSL and the sonochemical results mechanisms of the
reactions occurring in the cavitation bubbles are proposed (Fig.3).
Fig2. Peak height of NH emission in MBSL and sum of formation rates of NO2- and NO3- as a
function of N2 content in Ar at 359 kHz, Pac=59 W and T=11°C.
Fig3. Mechanism of formation of NO2- and NO3-.
References
[1] Navarro N. M., Pflieger R., Nikitenko S. I. Ultrason. Sonochem., 21 : 1026-1029, 2014.
[2] Z Machala, M Janda, K Hensel, I Jedlovský, L Leštinská, V Foltin, Journal of Molecular Spectroscopy
243 (2), 194-201 2007
[3] C Wang, N Srivastava The European Physical Journal D 60 (3), 465-477 2010
* E-mail: temim.ouerhani@cea.fr