Sonoluminescence Spectra Research Articles

P2 Naソノルミネセンススペクトルの希ガス効果と周波数依存性(ポスターセッション)

P2 Naソノルミネセンススペクトルの希ガス効果と周波数依存性(ポスターセッション)

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

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 (A3Π-X3Σ-) and OH (A2Σ+-X2Π). Both spectroscopic systems indicate the absence of thermal equilibrium during bubble collapse (Tv > Tr) 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 (C2Σ+-A2Σ+) and NH (c1Π-a1Δ) 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 H2 and N2H4, while no H2O2 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.

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

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.

Mechanism of two types of Na emission observed in sonoluminescence

The sonoluminescence (SL) spectrum of Na atoms revealed that the Na line consists of two components, one of which is a broadened component (broad component) which is shifted from the original D lines, and the other is an unshifted narrow component (narrow component). We spatially separated the continuum, broad, and narrow components by capturing SL images using different optical filters. We also temporally separated these components by measuring SL pulses using respective band-pass filters. The SL image distribution and the timing of the SL pulses were different between the broad and narrow components. The results suggested that the broad and narrow components of Na emission are generated from different bubble populations. The dependences of SL spectra on ultrasonic frequency and dissolved rare gas (He, Ne, Ar, Kr, and Xe) were also investigated. It is concluded that the broad component and a blue satellite peak at 558 nm originate from van der Waals molecules composed of Na and rare-gas atoms. The narrow component was predicted to occur under temperature conditions at bubble collapse higher than that for the broad component.

Effect of operational conditions on sonoluminescence and kinetics of H2O2 formation during the sonolysis of water in the presence of Ar/O2 gas mixture

Ultrasonic frequency is a key parameter determining multibubble sonoluminescence (MBSL) spectra of water saturated with Ar/O2 gas mixtures. At 20kHz, the MBSL is quenched by oxygen. By contrast, at high-frequency ultrasound the maximal MBSL intensity is observed in the presence of Ar/20%O2 gas mixture. Nevertheless, oxygen has no influence on the shape of MBSL spectra. The effect of oxygen on MBSL is explained by oxygen dissociation inside the collapsing bubble which is much more effective at high ultrasonic frequency compared to 20kHz ultrasound. In contrast to MBSL, a higher yield of H2O2 is observed in Ar/20%O2 gas mixture whatever the ultrasonic frequency. At 20°C and 20% of oxygen the maximal yield of H2O2 is observed at 204–362kHz. The maximal yield of H2O2 is shifted to 613kHz when the bulk temperature is raised up to 40°C. Coupling of high-frequency ultrasound with mechanical stirring and intensive Ar/O2 bubbling improves H2O2 production. Comparison of MBSL and sonochemistry allowed to conclude that H2O2 is formed from non-excited OH (X2Π) and HO2 radicals. Finally, it was shown that at the studied conditions the efficiency of ultrasonic degassing is hardly influenced by frequency.

Influence of ultrasonic frequency on Swan band sonoluminescence and sonochemical activity in aqueous tert-butyl alcohol solutions.

The multibubble sonoluminescence (MBSL) spectra of t-BuOH aqueous solutions submitted to power ultrasound at 20, 204, 362, and 613 kHz show emissions for the Δυ = -1 to Δυ = +2 vibrational sequences of C2* Swan system (d(3)Πg → a(3)Πu). The Δυ=+2 emission overlaps with the CH(A-X) emission band. The maximal Swan band emission is observed when the MBSL of water itself is almost completely quenched. In general, MBSL is more intense at high-frequency compared to 20 kHz ultrasound. However, in the presence of Xe, the MBSL of C2* at 20 kHz is so bright that it can be seen by the unaided eye as a blue glow in the close vicinity of the ultrasonic tip. The intensity of the C2* band emission exhibits a maximum vs t-BuOH concentration: 0.1-0.2 M at 20 kHz and (1-8) × 10(-3) M at high-frequency ultrasound. Such a huge difference is attributed to a much smaller bubble size at high ultrasonic frequency or, in other words, to a much higher bubble surface/volume ratio providing more efficient saturation of the bubble interior with t-BuOH vapors and to the fact that high frequency bubbles remain active for many more cycles than 20 kHz ones, thus accumulating more hydrocarbon decomposition products. Simulation of the emission spectra using Specair software demonstrated the absence of thermal equilibrium for C2* radicals (Tv > Tr), where Tv and Tr are the vibrational and the rotational temperature, respectively. In Ar, Tv decreases with increasing t-BuOH concentration reaching a steady value in the concentration domain that corresponds to C2* emission maximum intensity. In the presence of Xe an extremely high Tv is obtained, which is explained by the relatively low ionization potential of Xe providing a higher electron temperature of nonequilibrium plasma generated during bubble collapse. Analysis of the gaseous products of t-BuOH sonolysis reveals a significant sonochemical activity even at high t-BuOH concentration when MBSL is totally quenched, indicating that drastic conditions could be produced also within nonsonoluminescing cavitation bubbles.

The Ultraviolet Cutoff and Water Temperature Dependence of the Sonoluminescence Bubble Spectrum

In this paper, we calculate the emitted light spectrum from the sonoluminescence effect by considering that the vibration modes have a quantized energy like the nuclear energy levels in the collective model in nuclear physics. In this model we characterized the excited mode by the quantum angular momentum, so that the energy of the excited vibration modes comes from the surface vibration parameters of the bubble. We related these parameters to the surface tension of water. We assume that the vibration modes of the bubble with angular momentum J are excited by the acoustic wave and have a probability of excitation proportional to the acoustic wave frequency and angular momentum of the modes. So by using this assumption we tried to explain some characters of the sonoluminescence spectrum.

The influence of ultrasound frequency on the shape of the D-line of Na in the sonoluminescence spectra of aqueous solutions of sodium chloride and sodium dodecylsulfate

The multibubble sonoluminescence spectra of aqueous solutions of sodium chloride and sodium dodecylsulfate saturated with argon were measured around the D-line of Na under irradiation with ultrasound with a frequency of 20 and 870 kHz. The Na line had a complex shape and incorporated two overlapping components: an asymmetrically broadened shifted band and a narrow unshifted doublet. The Na line in the spectra of the dodecylsulfate solution was notably narrower than the line in the NaCl solution spectra at both ultrasound frequencies. At the same time, the changes in the line shape observed upon the transition from one frequency to the other in these two solutions were similar. The line was narrower and had a prominent narrow component at a frequency of 870 kHz, and the line was broader with a dominant broad component at a frequency of 20 kHz. The results are discussed within the context of different dynamics of bubbles at high and low ultrasound frequencies.

Two components of Na emission in sonoluminescence spectrum from surfactant aqueous solutions

Sonoluminescence from sodium dodecyl sulfate (SDS) aqueous solutions exhibits Na emission. The spectrum of Na emission was measured as a function of sonication time for a total of 30min at an ultrasonic frequency of 148kHz. The spectral line profiles changed with the sonication time, suggesting that the Na emission consists of two components: broadened lines, which are shifted from the original D lines, and unshifted narrow lines. The intensity of the unshifted narrow lines decreased at a greater rate than that of the broadened lines with increasing sonication time. This effect was enhanced at a higher acoustic power. The shifted broadened lines remained after sonication for 30min. We propose that these quenching effects are caused by the accumulation of gases decomposed from SDS molecules inside bubbles. The CO2 gas dependence of Na emission in NaCl aqueous solutions showed a similar change in the line profiles to that in SDS aqueous solutions, which supported this proposition. The unshifted narrow lines are easily affected by foreign gases. The results suggest that the two components originate from different environments around the emitting species, although both of them originate from the gas phase inside bubbles. The generation mechanisms of the two components are discussed.

Activating molecules, ions, and solid particles with acoustic cavitation.

The chemical and physical effects of ultrasound arise not from a direct interaction of molecules with sound waves, but rather from the acoustic cavitation: the nucleation, growth, and implosive collapse of microbubbles in liquids submitted to power ultrasound. The violent implosion of bubbles leads to the formation of chemically reactive species and to the emission of light, named sonoluminescence. In this manuscript, we describe the techniques allowing study of extreme intrabubble conditions and chemical reactivity of acoustic cavitation in solutions. The analysis of sonoluminescence spectra of water sparged with noble gases provides evidence for nonequilibrium plasma formation. The photons and the "hot" particles generated by cavitation bubbles enable to excite the non-volatile species in solutions increasing their chemical reactivity. For example the mechanism of ultrabright sonoluminescence of uranyl ions in acidic solutions varies with uranium concentration: sonophotoluminescence dominates in diluted solutions, and collisional excitation contributes at higher uranium concentration. Secondary sonochemical products may arise from chemically active species that are formed inside the bubble, but then diffuse into the liquid phase and react with solution precursors to form a variety of products. For instance, the sonochemical reduction of Pt(IV) in pure water provides an innovative synthetic route for monodispersed nanoparticles of metallic platinum without any templates or capping agents. Many studies reveal the advantages of ultrasound to activate the divided solids. In general, the mechanical effects of ultrasound strongly contribute in heterogeneous systems in addition to chemical effects. In particular, the sonolysis of PuO2 powder in pure water yields stable colloids of plutonium due to both effects.

Effects of argon sparging rate, ultrasonic power, and frequency on multibubble sonoluminescence spectra and bubble dynamics in NaCl aqueous solutions

The sonoluminescence spectra from acoustic cavitation in aqueous NaCl solutions are systematically studied in a large range of ultrasonic frequencies under variation of electrical power and argon sparging. At the same time, bubble dynamics are analysed by high-speed imaging. Sodium line and continuum emission are evaluated for acoustic driving at 34.5, 90, 150, 365, and 945kHz in the same reactor vessel. The results show that the ratio of sodium line to continuum emission can be shifted by the experimental parameters: an increase in the argon flow increases the ratio, while an increase in power leads to a decrease. At 945kHz, the sodium line is drastically reduced, while the continuum stays at elevated level. Bubble observations reveal a remarkable effect of argon in terms of bubble distribution and stability: larger bubbles of non-spherical shapes form and eject small daughter bubbles which in turn populate the whole liquid. As a consequence, the bubble interactions (splitting, merging) appear enhanced which supports a link between non-spherical bubble dynamics and sodium line emission.

Analysis of Sonoluminescence Signal from Megasonic Irradiated Gas-Containing Aqueous Solutions Using Replaceable Single-Band Filters

A simple method to resolve the features that are characteristic of hydroxyl radicals in sonoluminescence (SL) spectra from aqueous solutions has been developed. Using a modified version of cavitation threshold (CT) cell in which single band filters were sandwiched between the UV grade fused silica window and the photomultiplier tube (PMT) in the cell, photon emission in the wavelength range of 280 to 400 nm was measured. Four different single band filters, 280–305.5 nm, 300–340 nm, 335–375 nm and 374.5–397.5 nm were used. The results for air and Ar saturated DI water are consistent with those reported in the literature and obtained using expensive spectrometers. The SL signal collected in ammonium hydroxide solutions indicated that at higher power densities the signal intensity may not be relatable to the generation rate of hydroxyl radicals in their ground state.

Multibubble sonoluminescence as a tool to study the mechanism of formic acid sonolysis

Sonoluminescence spectra collected from 0.1 to 3.0M aqueous solutions of formic acid sparged with argon show the OH(A2Σ+−X2Πi) and C2(d3Πg→a3Πu) emission bands and a broad continuum typical for multibubble sonoluminescence. The overall intensity of sonoluminescence and the sonochemical yield of HCOOH degradation vary in opposite directions: the sonoluminescence is quenched while the sonochemical yield increases with HCOOH concentration. By contrast, the concentration of formic acid has a relatively small effect on the intensity of C2 Swan band. It is concluded that C2 emission originates from CO produced by HCOOH degradation rather than from direct sonochemical degradation of HCOOH. The intensity of C2 band is much stronger at high ultrasonic frequency compared to 20kHz ultrasound which is in line with higher yields of CO at high frequency. Another product of HCOOH sonolysis, carbon dioxide, strongly quenches sonoluminescence, most probably via collisional non-radiative mechanism.

Changes in the shape of atomic lines of alkali metals in sonoluminescence spectra of solutions of surfactants and halogenides

The multibubble sonoluminescence spectra of aqueous solutions of sodium dodecyl sulfate, of the mixture of sodium dodecyl sulfate with lithium and potassium chlorides, and of sodium and potassium halogenides were measured near the lines of metals at an ultrasonic frequency of 20 kHz. The Na, Li, and K lines in spectra of surfactant solutions are noticeably narrower than those obtained in solutions of metal chlorides. The width of Na lines in spectra of metal fluorides, chlorides, and iodides remains constant, while that of the K line increases with increasing atomic weight of a halogen. The results are discussed in the context of the effect that the bonding strength of an atom possibly has on the formation of metal lines in sonoluminescence spectra.

Non-Boltzmann Population Distributions during Single-Bubble Sonoluminescence

Single-bubble sonoluminescence (SBSL) spectra from aqueous sulfuric acid solutions containing dissolved neon show widely varying emission despite being similar in chemical composition. From a 65 wt % solution, emission from hydroxyl radicals is observed, with the rovibronic progression being well-described by a single temperature of 7600 K. From an 80 wt % solution, however, emission spectra reveal vibrationally hot sulfur monoxide (SO; Tv = 2400 K) that is also rotationally cold (Tr = 280 K). Further, the SO vibrational population distribution is best-described by a non-Boltzmann distribution. Excited neon atom emission observed from the 80 wt % solution gives an estimated temperature of only 3400 K, indicative of emission from a cool outer shell at the interfacial region. The neon atom excited-state population is also best-described by a non-Boltzmann distribution. These observations are consistent with SBSL emission having both a spatial and temporal component, and the implications for these effects are discussed.

Use of a Simple Cavitation Cell Set-Up with Replaceable Single Band Filters for Analysis of Sonoluminescence Signal from Megasonic Irradiated Gasified Aqueous Solutions

A simple method to resolve the features that are characteristic of hydroxyl radicals in sonoluminescence (SL) spectra from aqueous solutions has been developed. Using a modified version of cavitation threshold (CT) cell in which single band filters were sandwiched between the UV grade fused silica window and the photomultiplier tube (PMT) in the cell, photon emission in the wavelength range of 280 to 400 nm was measured. Four different single band filters, 280 – 305.5 nm, 300 – 340 nm, 335 – 375 nm and 374.5 – 397.5 nm were used. The results for air and Ar saturated DI water are consistent with those reported in the literature and obtained using expensive spectrometers. The SL signal collected in ammonium hydroxide solutions indicated that at higher power densities the signal intensity may not be relatable to the generation rate of hydroxyl radicals in their ground state.

The Origin of Isotope Effects in Sonoluminescence Spectra of Heavy and Light Water

Bubble and peak: The isotope effects in the sonoluminescence spectra of light and heavy water under ultrasound indicate the formation of a non-equilibrium plasma inside the collapsing cavitation bubbles. The picture demonstrates the active cavitation zones in water at 204 kHz.

Characteristic spectra of single-bubble sonoluminescence in the rare-earth salt aqueous solutions

The single-bubble sonoluminescence spectra of the terbium chloride aqueous solutions dissolved with the noble gas Ar are studied in this paper. Under the condition of fixed driving ultrasonic frequency and different sound pressures, a series of line spectra is identified as emissions from the transitions of OH radical vibrational levels from the first excited state A2∑+ to the ground state X2Π, including (0, 0) transition at 307 nm, (0, 1) transition at 335 nm and (1, 0) transition at 276 nm and so on. The experimental results show that higher sound pressure is conducive to the appearance of the line spectrum at 276 nm while lower sound pressure is favorable for the appearance of the line spectra at 307 nm and 335 nm. The relative intensity of the line spectrum in the total spectrum is expressed quantificationally by defining an intensity ratio of the line spectrum to the continuous spectrum. In addition, the effects of the driving sound pressure on the intensity ratios of different line spectra are given.

Temperature Nonequilibration during Single-Bubble Sonoluminescence.

Single-bubble sonoluminescence (SBSL) spectra from liquids having low vapor pressures, especially mineral acids, are exceptionally rich. During SBSL from aqueous sulfuric acid containing dissolved neon, rovibronic emission spectra reveal vibrationally hot sulfur monoxide (SO; Tv = 2100 K) that is also rotationally cold (Tr = 290 K). In addition to SO, excited neon atom emission gives an estimated temperature, for neon, of several thousand Kelvin. This nonequilibrated temperature is consistent with dynamically constrained SO formation at the liquid-vapor interface of the collapsing bubble. Formation occurs via collisions of fast neon atoms (generated within the collapsing bubble) with liquid-phase molecular species in the interfacial region, thus allowing for a mechanistic understanding of the processes leading to light emission.

Temperature and intensity of sonoluminescence radiation in sulfuric acid

The spectral radiation of sonoluminescence (SL) from sulfuric acid doped with various Xe concentrations has been studied in a hydrochemical simulation, including radiation effects of both continuum and line emissions. The simulation considers the same temperature for both continuum and line parts of the SL spectrum and gives results in agreement with the experiment. Also, it can properly show period-doubling dynamics for a 50 torr bubble. For most of the allowable driving pressures, it is shown that both the temperature and the intensity of SL for a 4 torr bubble are greater than those of a 50 torr bubble. However, for the range of pressures near the maximum driving conditions of the 50 torr bubble, the SL intensity of this bubble can be up to three orders of magnitude greater than the 4 torr bubble. This case, which is in agreement with the experiment, is obtained when the light-emitting region of the 50 torr bubble is about three orders of magnitude greater than the 4 torr bubble.