Use of NH (A³Π–X³Σ⁻) sonoluminescence for diagnostics of nonequilibrium plasma produced by multibubble cavitation

Abstract

In this work, the sonoluminescence of NH radicals has been evaluated as a new spectroscopic probe for the nonequilibrium plasma produced by multibubble cavitation in liquids. The experiments were performed in aqueous ammonia solutions subjected to power ultrasound at low and high frequencies and under two different rare gases (Ar and Xe). Sonoluminescence (SL) spectroscopy focuses on the emission of the two present systems: NH (AΠ-XΣ) and OH (AΣ-XΠ). Both spectroscopic systems indicate the absence of thermal equilibrium during bubble collapse (T > T) irrespective of the saturating gas. When Ar is used as the saturating gas, these emissions can be fitted using Specair software and the corresponding rovibronic temperatures are derived. Both species indicate a net increase in vibrational temperatures with the US frequency. In Xe, the SL spectra exhibit OH (CΣ-AΣ) and NH (cΠ-aΔ) emission bands indicating a higher electron temperature compared to Ar. However, in Xe, the SL spectra cannot be satisfactorily fitted because of significant line broadening. The estimation of the intrabubble pressure via SL simulation using Specair software is discussed. Monitoring of the sonochemical activity indicates the formation of H and NH, while no HO accumulates under these conditions. In the presence of Xe, NO is also formed as a sonolysis product. The appearance of new possible reaction pathways under Xe is made possible by the higher plasma electron density and correlates with SL data.

Turning single bubble sonoluminescence from blue in pure water to green by adding trace amount of carbon nanodots

“…Such a feature can be attributed to the coupling of CNDs with hydroxyl radicals. The emission around 340 nm can also come from NH as reported by R. Pflieger, et al [43] . Because the possibility for OH • (v:1–0) transition is relatively low, a more reasonable mechanism for strong emission at 340 nm shown in Fig.…”

“…Similar broadband emission from CO molecular has been reported by Pflieger et al in SL at high acoustic driving frequency [56] . It is expected that better resolution of the emission lines from a molecular can be achieved at a low driving frequency [43] . In this study, the spectral resolution of the spectrometer is 1 nm which is not high enough to reveal the fine structure of SL spectrum.…”

Diagnosing the plasma formed during acoustic cavitation in [BEPip][NTf2] ionic liquid

“…In a 0.1 M ammonia solution, vibrational temperatures of 9000 ± 1000 K for OH (A 2 Σ+-X 2 Π) and 7000 ± 1000 K for NH (A 3 Π-X 2 Σ -) were estimated. 21 Concerning concentrated acids, Ar (4p-4s) emission in sulfuric acid corresponded to an electronic temperature of 8000 K, while in phosphoric acid OH (A 2 Σ + -X 2 Π) and PO (B 2 Σ + -X 2 Π) indicated vibrational temperatures of 9500 K and 4000 K, respectively. All these temperatures show a strong similarity, although more extreme conditions would be expected for IL (and concentrated acids, that share with IL a very low vapor pressure) than for aqueous solutions.…”

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

“…MBSL spectra of argon-saturated 0.1M NH3⋅H2O solution exhibit OH(A 2 Σ + -X 2 Π) and NH(A 3 Π-X 3 Σ -) emissions and a broad continuum as well ( Fig. 2) [10]. At 20 kHz, the NH(A 3 Π-X 3 Σ -) system exhibits well-resolved (0-0)Q and (1-1)Q vibrational branches.…”