Emission from Electronically Excited Metal Atoms during Single-Bubble Sonoluminescence

Flannigan, David J.; Suslick, Kenneth S.

doi:10.1103/physrevlett.99.134301

Cited by 67 publications

(72 citation statements)

References 38 publications

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“…Due to their high emission power, noble gas bubbles in acids are ideal candidates for sonoluminescence studies, and the literature on such experiments is continuously growing. For SL in H 2 SO 4 , see for instance [8,9,10,11,12,13,14,15,16,18,17,19,20,21,22,23,24,25,26,27]. The basic mechanism of light emission in the acids is believed to be similar to that observed in other liquids like water (see e.g.…”

Section: Introductionmentioning

confidence: 90%

“…A potential micro spray would (fully or partly) evaporate with subsequent thermolysis, reduction, and excitation of the metal in the heated (and possibly plasma) environment inside the bubble. Indeed, some results indicate an intimate connection of non-spherical bubble dynamics or bubble motion [20] and alkali metal line emissions, which points to some liquid injection mechanism. In experiments where emissions with and without lines appear at different spatial locations, a closer investigation of the bubble dynamics leading to the different SL activity is possible.…”

Section: Introductionmentioning

confidence: 96%

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Sonoluminescence and dynamics of cavitation bubble populations in sulfuric acid

Thiemann

Holsteyns

Cairós

et al. 2017

Ultrasonics Sonochemistry

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The detailed link of liquid phase sonochemical reactions and bubble dynamics is still not sufficiently known. To further clarify this issue, we image sonoluminescence and bubble oscillations, translations, and shapes in an acoustic cavitation setup at 23kHz in sulfuric acid with dissolved sodium sulfate and xenon gas saturation. The colour of sonoluminescence varies in a way that emissions from excited non-volatile sodium atoms are prominently observed far from the acoustic horn emitter ("red region"), while such emissions are nearly absent close to the horn tip ("blue region"). High-speed images reveal the dynamics of distinct bubble populations that can partly be linked to the different emission regions. In particular, we see smaller strongly collapsing spherical bubbles within the blue region, while larger bubbles with a liquid jet during collapse dominate the red region. The jetting is induced by the fast bubble translation, which is a consequence of acoustic (Bjerknes) forces in the ultrasonic field. Numerical simulations with a spherical single bubble model reproduce quantitatively the volume oscillations and fast translation of the sodium emitting bubbles. Additionally, their intermittent stopping is explained by multistability in a hysteretic parameter range. The findings confirm the assumption that bubble deformations are responsible for pronounced sodium sonoluminescence. Notably the observed translation induced jetting appears to serve as efficient mixing mechanism of liquid into the heated gas phase of collapsing bubbles, thus potentially promoting liquid phase sonochemistry in general.

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Section: Introductionmentioning

confidence: 90%

Section: Introductionmentioning

confidence: 96%

Sonoluminescence and dynamics of cavitation bubble populations in sulfuric acid

Thiemann

Holsteyns

Cairós

et al. 2017

Ultrasonics Sonochemistry

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“…7 Similarly, it has long been recognized that nonvolatiles can undergo sonochemical reactions. 5,8 There are two models proposed to explain how nonvolatile species get heated in a collapsing bubble: the shell model and the injected droplet model, as illustrated in Figure 1.…”

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confidence: 99%

“…7 Observation of the exciplex suggests that the emitting Na* atoms are in a gas phase state, regardless of their origin.…”

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confidence: 99%

“…In SBSL, only moving single bubbles will undergo sufficient deformation to provide for nanodroplet injection and only moving single bubbles give emission from nonvolatile precursors. 7 In our bubble clouds, we estimate from the streak length of individual bubble emission from photographs with a known shutter speed that bubbles near the horn move only ∼4 mm/s, whereas the Na* emitting bubble far from the horn move at ∼17 mm/s (SI Figure S6). In cavitating bubble clouds, there are two distinct populations of cavitation events: (1) bubbles near the vibrating horn that are relatively stationary (probably due to interbubble Bjerknes forces), whose collapse is highly symmetric which produces a hotter core and only continuum emission, and (2) rapidly moving bubbles in a streaming liquid flow outside of the dense clouds, whose collapse is much less symmetric and from which emission from nonvolatiles becomes possible through the mechanism of nanodroplet injection (Figure 1).…”

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confidence: 99%

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Spatial Separation of Cavitating Bubble Populations: The Nanodroplet Injection Model

2009

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Multibubble sonoluminescence (MBSL), the light emitted during the implosive collapse of clouds of bubbles in liquids irradiated with high-intensity ultrasound, is a consequence of acoustic cavitation and has been known for more than 70 years, 1 but only recently have we begun to quantify the conditions created in the gas phase of the collapsing bubble. 2 Our previous investigation on single-bubble sonoluminescence (SBSL) and MBSL in sulfuric acid revealed that an optically opaque plasma core was generated in submicron collapsing bubbles in both SBSL 3 and MBSL, 4 with effective emission temperatures inside the collapsing bubbles approaching 20 000 K.The origin of the unexpected emission from nonvolatile species during MBSL, however, remains a central question in the mechanism of acoustic cavitation; two general models for the sonochemistry and sonoluminescence of nonvolatiles have been proposed, as shown in Figure 1, but no previous work has been able to differentiate between them. 5 We report here the direct observation of spatial separation of two types of sonoluminescing bubbles during MBSL: those that show emission from Na* D line emission in Na 2 SO 4 solutions in sulfuric acid and others that do not. As discussed below, this result is consistent only with nanodroplet injection during cavitation ( Figure 1).When nonvolatile metal ions are present in an aqueous solution irradiated with ultrasound, excited-state metal atom emission can be observed in both MBSL 6 and (in sulfuric acid) SBSL. 7 Similarly, it has long been recognized that nonvolatiles can undergo sonochemical reactions. 5,8 There are two models proposed to explain how nonvolatile species get heated in a collapsing bubble: the shell model and the injected droplet model, as illustrated in Figure 1. In the shell model, the metal ions in the initially liquid interfacial region are reduced and excited by radicals formed in the gas phase. In the injected droplet model, interfacial instabilities (capillary surface waves and microjet formation 5,9,10 ) during bubble collapse are proposed to nebulize nanodroplets of liquid into the hot core of the collapsing bubble, with subsequent thermolysis and reduction of nonvolatile metal ions and excited metal atom emission. Direct experimental evidence in favor of one or the other model, however, has been difficult to obtain. Hydrodynamic calculations 5c suggest that the interfacial region between the bulk liquid and the gas phase inside the bubble remains relatively cool, but issues of vapor supersaturation and microjetting during collapse are complex. 9 As shown in Figure 2A, we observe two spatially separate types of MBSL from 0.1 M Na 2 SO 4 in 95% sulfuric acid: (1) blue-white emission near the horn and (2) orange emission (from electronically excited Na* atom D lines) further away (cf. Supporting Information (SI) for experimental details). We have previously observed 4 three different light emitting regimes upon varying the acoustic intensity: filamentous (<16 W/cm 2 ), bulbous (16-24 W/cm 2 ), and con...

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