Spectroscopy of Sonoluminescence and Sonochemistry in Water Saturated with N₂–Ar Mixtures

Abstract

Sonoluminescence spectra in relation with sonochemical activity of water sparged with Ar/N2 gas mixtures were systematically studied at two ultrasonic frequencies (20 and 359 kHz). At 20 kHz, solely the molecular emission of OH (A(2)Σ(+)-X(2)Πi) is observed in addition to a broad continuum typical for multibubble sonoluminescence. On the contrary, at high frequency a second emission band is present around 336 nm which is assigned to the NH (A(3)Π-X(3)Σ(-)) system. In addition, the sonolysis of a 0.2 M NH3·H2O solution at 359 kHz in the presence of pure Ar yields the emission bands of NH (A(3)Π - X(3)Σ(-)) (336 nm) and NH (C(1)Π-A(1)Δ) (322 nm) systems confirming the sonochemical production of NH radicals. The N2 (C(3)Πu-B(3)Πg) emission band is absent at both frequencies. This uncommon phenomenon can be explained by the quenching of the N2 (C(3)Πu) excited state with water molecules inside the bubbles. The sonoluminescence of NH radicals at 359 kHz indicates more effective intrabubble dissociation of N2 molecules at high ultrasonic frequency compared to low-frequency (20 kHz) ultrasound. Its absence at 20 kHz may also be related to strong quenching, e.g., by water molecules. The kinetic study of the formation of principal sonochemical products (H2, H2O2, HNO3, HNO2) confirmed the more drastic conditions produced during bubble collapse at higher ultrasonic frequency.

Controlling of reactive species in atmospheric Ar bubble discharge by adding N2/O2a

“…A similar trend of OH (A–X) was reported by Ouerhani et al using multi‐bubble sonoluminescence in water saturated with N 2 ‐Ar gaseous mixtures. They claimed that for high N 2 content, the decrease is due to the quenching of OH with N 2 molecules, and for low N 2 concentration, this quenching effect is counterbalanced by a lesser recombination of OH + H radicals due to scavenging of H by N and N 2 , and hence OH emission becomes higher . In addition, the simulated results reported by Tian et al using two‐dimensional plasma hydrodynamics simulation show that the emission intensity of OH (A–X) with Ar bubble is higher than that with N 2 bubble under low voltage, while that is higher with N 2 bubble under high voltage .…”

“…The rising trend of intensities at 1% N 2 proportion could be explained by the change of reaction and discharge power induced by little amount of N 2 added. A similar trend of OH (A-X) was reported by Ouerhani et al [29] using multi-bubble sonoluminescence in water saturated with N 2 -Ar gaseous mixtures. They claimed that for high N 2 content, the decrease is due to the quenching of OH with N 2 molecules, and for low N 2 concentration, this quenching effect is counterbalanced by a lesser recombination of OH + H radicals due to scavenging of H by N and N 2 , and hence OH emission becomes higher.…”

“…They claimed that for high N 2 content, the decrease is due to the quenching of OH with N 2 molecules, and for low N 2 concentration, this quenching effect is counterbalanced by a lesser recombination of OH + H radicals due to scavenging of H by N and N 2 , and hence OH emission becomes higher. [29] In addition, the simulated results reported by Tian et al [24] using two-dimensional plasma hydrodynamics simulation show that the emission intensity of OH (A-X) with Ar bubble is higher than that with N 2 bubble under low voltage, while that is higher with N 2 bubble under high voltage . Thus it is reasonable that 1% N 2 added in Ar bubble discharge leads to the increase of OH (A-X), where the discharge power is found to be maximal in our experiment.…”

Spectroscopic Studies of Nonequilibrium Plasma Generated by Acoustic Cavitation in Aqueous Solutions

“…Higher vibrational temperature highlights more drastic intrabubble conditions at higher ultrasonic frequency. This conclusion is in full agreement with MBSL study in water saturated with N2-Ar gas mixture [12]. At 20 kHz, solely the molecular emission of OH(A 2 Σ + −X 2 Πi) is observed in addition to a broad 10th International Symposium on Cavitation -CAV2018 Baltimore, Maryland, USA, May 14 -16, 2018 CAV18-05190 continuum typical for multibubble sonoluminescence.…”

A parametric review of sonochemistry: Control and augmentation of sonochemical activity in aqueous solutions

“…This decreasing trend is also seen for oxygen and argon atmospheres, however for nitrogen there is an initial small increase followed by a gradual increase [91]. The effect of decreasing pH with sonication in air is due to the •OH radicals oxidising nitrogen, resulting in the formation of nitrous and nitric acids [247]. However, in air-saturated aqueous NaOH (pH 12) sonication resulted in the formation of the peroxynitrite anion, likely to be produced from the superoxide radical formed in the basic conditions [248].…”