Sonoluminescence Spectra Research Articles

Effects of Rare Gases on Sonoluminescence Spectrum of the K Atom

Multibubble-sonoluminescence spectra from Ar-saturated KCl aqueous solutions were measured in the temperature range of 15-40 °C at frequencies of 48 kHz, 148 kHz, and 1 MHz. The effects of dissolved rare gases and the ultrasonic frequency on the shape of the K atom emission spectrum were examined. The line width of the K doublet was independent of the solution temperature, whereas the K line intensity decreased with increasing temperature. The spectra from Xe- and Ar-saturated solutions at 148 kHz exhibited a red-shifted and asymmetrically broadened doublet of K lines. The spectrum from a He-saturated solution, on the other hand, exhibited symmetrically broadened K lines, which were slightly blue-shifted. The observed effects of rare gases are in good agreement with those obtained by gas-phase spectroscopy. These results strongly indicate that the excited K atoms are perturbed by rare gases inside bubbles. The spectra from Xe- and Ar-saturated solutions also indicated that the K doublet is composed of two types of peaks, shifted broadened lines and unshifted narrow lines. These two types of peaks were clearly separated at a frequency of 48 kHz with a high acoustic power in the case of Ar-saturated solutions. The intensity of the broadened lines relative to that of the narrow lines markedly decreased at 1 MHz. Although the narrow lines as well as the broadened lines may have originated from inside the bubbles, the exact mechanism is still unclear.

Nonequilibrium Vibrational Excitation of OH Radicals Generated During Multibubble Cavitation in Water

The sonoluminescence (SL) spectra of OH(A(2)Σ(+)) excited state produced during the sonolysis of water sparged with argon were measured and analyzed at various ultrasonic frequencies (20, 204, 362, 609, and 1057 kHz) in order to determine the intrabubble conditions created by multibubble cavitation. The relative populations of the OH(A(2)Σ(+)) v' = 1-4 vibrational states as well as the vibronic temperatures (T(v), T(e)) have been calculated after deconvolution of the SL spectra. The results of this study provide evidence for nonequilibrium plasma formation during sonolysis of water in the presence of argon. At low ultrasonic frequency (20 kHz), a weakly excited plasma with Brau vibrational distribution is formed (T(e) ~ 0.7 eV and T(v) ~ 5000 K). By contrast, at high-frequency ultrasound, the plasma inside the collapsing bubbles exhibits Treanor behavior typical for strong vibrational excitation. The T(e) and T(v) values increase with ultrasonic frequency, reaching T(e) ~ 1 eV and T(v) ~ 9800 K at 1057 kHz.

Multibubble sonoluminescence of Tb3+ ion in aqueous solutions of dimethyl sulfoxide

The intensity and spectra of multibubble sonoluminescence of TbCl3 solutions in water-DMSO mixtures saturated with air and argon are studied. The spectra represent the superposition of the characteristic glow of Tb3+ ions and the continuum of emission of electronically excited products of solvent sonolysis (with H2O*, OH*, and SO2* as main emitters). Abnormal action of DMSO and sulfur dioxide on the characteristic luminescence of Tb3+ ions during sonolysis of aqueous solutions is revealed. These additives enhance the sonoluminescence of water to different extent, quench the sonoluminescence of Tb3+, and differently influence the photoluminescence quantum yield of this ion (DMSO acts as activator, whereas SO2 acts as quencher). Sulfur dioxide quenches the sonoluminescence of Tb3+ much more efficiently than the photoluminescence of Tb3+. The abnormal effect of DMSO on sonoluminescence is most probably due to the quenching action of sulfur dioxide formed during sonolysis of DMSO on Tb3+* ions in cavitation bubbles.

Simple model of Na D-line shape in sonoluminescence spectra

A model explaining the Na D-line shape in sonoluminescence (SL) spectra is proposed, which is based on the hypothesis that a complicated profile of this line (involving shift, broadening, asymmetry, and parent emission peaks) is formed due to superposition of the spectra of SL generated at different densities of a perturbing medium. Simulations of the experimental spectra by model allow one to make a conclusion about the character of density variations during the emission, and to determine the interval of densities in which the emission from Na atoms occurs. In this same context, the profile of the potassium SL line is considered. It is suggested that the proposed model is applicable to any atoms in a dense variable environment.

1J4-4 Sonication-time dependence of sonoluminescence spectrum from Na atom in surfactant solutions(Nonlinear Acoustics, High Power Ultrasound, Sonochemistry)

1J4-4 Sonication-time dependence of sonoluminescence spectrum from Na atom in surfactant solutions(Nonlinear Acoustics, High Power Ultrasound, Sonochemistry)

Multi-bubble sonoluminescence of phosphoric acid

Multi-bubble sonoluminescence spectra of 85% H3PO4 and the dependences of sonoluminescence intensity on the acid concentration and temperature are obtained. The spectra contain a weakly structured 300–600-nm band formed by the superposition of radiation from several emitters (presumably, oxygencontaining products of acid sonolysis, viz., PO, HOPO, and PO2). Weak luminescence at a wavelength exceeding 600 nm can be due to emission from excited O* and Ar* atoms. The shape of the fundamental band changes upon a transition from multi-bubble sonolysis to sonolysis in the setup for one-bubble sonoluminescence, in which several clusters of cavitation bubbles are formed in a spherical flask at ultrasonic frequencies multiple of the first acoustic resonance frequency (multi-cluster sonoluminescence). The form of the temperature dependence of the sonoluminescence intensity depends on the detection regime: for natural heating of 85% acid under the action of ultrasound, a curve with a luminescence peak at 40°C is observed, while in detection with preliminary thermostating “over points,” only an inflection exists on a monotonic curve describing a decrease of intensity upon heating. An analogous curve for acids with a lower viscosity (hydrochloric and nitric acids) has neither a peak nor inflection irrespective of the detection regime. It is concluded that the viscosity of phosphoric acid plays a decisive role in the evolution of cavitation and in obtaining intense sonoluminescence.

Data collapse of the spectra of water-based stable single-bubble sonoluminescence

In the early days of stable single-bubble sonoluminescence, it was strongly debated whether the emission was blackbody radiation or whether the bubble was transparent to its own radiation (volume emission). Presently, the volume emission picture is nearly universally accepted. We present new measurements of spectra with apparent color temperatures ranging from 6000 to 21 000 K. We show through data collapse that within experimental uncertainty, apart from a constant, the spectra of strongly driven stable single-bubble sonoluminescence in water can be written as the product between a universal function of wavelength and a functional form that only depends on wavelength and apparent temperature but has no reference to any other parameter specific to the experimental situation. This remarkable result does question our theoretical understanding of the state of the plasma in the interior of strongly driven stable sonoluminescent bubbles.

Sonoluminescence from OH(C2Σ+) and OH(A2Σ+) Radicals in Water: Evidence for Plasma Formation during Multibubble Cavitation

Bubble trouble: Multibubble sonoluminescence spectra in water under Kr and Xe present emission lines of OH(C2Σ+–A2Σ+). This band, never observed in flames, indicates plasma formation in the collapsing bubbles.

Characterization of Acoustic Cavitation Bubbles in Different Sound Fields

Various fundamental properties of acoustic cavitation bubbles have been investigated in single- and dual-frequency sound fields. It was found that the relative extent of bubble coalescence in the dual-frequency field correlated strongly with the synergistic enhancement of the sonochemical reaction rates. Both the relative extent of coalescence and the sonochemical synergy observed were enhanced through the addition of coalescence-inhibiting solutes. This was attributed to greater nucleation in the dual-frequency mode compared with the single-frequency modes, producing a very localized and high-density bubble field. The acoustic bubble size, compared with that measured at 355 kHz alone, was found to increase upon the application of synchronous 20 kHz pulses but was reduced dramatically when the low frequency was applied as a continuous wave. This trend is consistent with previous reports indicating that the bubble density and cavitation activity are relatively higher in the pulsed system and that the continuous wave application exerts a strong cancellation effect. The changes in bubble density and coalescence rates are proposed to govern the acoustic bubble size. The bubble lifetime was found to be longer in the dual-frequency field (>0.30 ms; >6 low-frequency oscillations, >100 high-frequency oscillations) compared with both single-frequency fields (0.26 ms and 5 oscillations for the low frequency; 0.22 ms and 75 oscillations for the high frequency). The confluence of a longer bubble lifetime and more asymmetric collapse conditions, the latter inferred from a more pronounced sodium atom emission in the sonoluminescence spectrum, resulted in a lower bubble collapse temperature measured in the dual-frequency system.

Molecular Emission and Temperature Measurements from Single-Bubble Sonoluminescence

Single-bubble sonoluminescence (SBSL) spectra in H2O show featureless continuum emission. From an acoustically driven, moving bubble in phosphoric acid (H3PO4), we observe very strong molecular emission from excited OH radicals (∼310 nm), which can be used as a spectroscopic thermometer by fitting the experimental SBSL spectra to the OH A 2Σ+ - X 2Π rovibronic transitions. The observed emission temperature (T(em)) ranges from 6200 to 9500 K as the acoustic pressure (P(a)) varies from 1.9 to 3.1 bar and from 6000 to >10,000 K as the dissolved monatomic gas varies over the series from He to Xe.

Multibubble sonolysis and sonoluminescence in molten elementary sulfur and sulfur—styrene mixture

The effect of saturation with argon, as well as styrene and iodine additives on the temperature dependence of multibubble sonoluminescence intensity in molten sulfur at 120–230 °C was studied. The shape of the temperature dependence with a maximum at 170–200 °C is determined by the viscosity variations related to the changes in the molecular structure of molten elemental sulfur. At high temperatures, cyclooctasulfane (S8) molecules break to radical products, which then undergo polymerization that can be slowed down by the additives. Sulfurization of styrene during sonolysis of a sulfur—styrene mixture resulting in products of the thiophene series was detected. Unlike thermal sulfurization that affords 2,5-diphenylthiophene as a major product, sonochemical sulfurization results mainly in 2,4-diphenylthiophene. The mechanism of 2,4-diphenylthiophene formation initiated by the reaction of styrene molecules with S+ ions produced upon fragmentation of S8 within cavitation bubbles is proposed. The glow of electronically excited S+* ions is responsible for the band with a maximum at 560 nm in the sonoluminescence spectrum of molten sulfur, which is suppressed by the styrene additive.

Diagnosing temperature change inside sonoluminescing bubbles by calculating line spectra

With the numerical calculation of the spectrum of single bubble sonoluminescence, we find that when the maximum temperature inside a dimly luminescing bubble is relatively low, the spectral lines are prominent. As the maximum temperature of the bubble increases, the line spectrum from the bright bubble weakens or even fades away relative to the background continuum. The calculations in this paper effectively interpret the observed phenomena, indicating that the calculated results, which are closely related to the spectrum profile, such as temperature and pressure, should be reliable. The present calculation tends to negate the existence of a hot plasma core inside a sonoluminescing bubble.

Spatiotemporal Separation of Na-Atom Emission from Continuum Emission in Sonoluminescence

The spectrum of multi-bubble sonoluminescence (MBSL) from alkali-metal aqueous solutions consists of continuum emission and line emission from alkali-metal atoms. We performed spatiotemporal separation of the two types of emission to investigate origin of the emissions. Images of MBSL at 137 kHz from NaCl solution taken with a digital camera were analyzed to obtain red and blue components. The red component corresponds to the Na-atom emission (Na D lines), and the blue one to the continuum emission. The spatial range of the Na-atom emission in the images extended wider than that of the continuum emission. Spectrally divided optical pulses of sonoluminescence were observed using a high-sampling-rate oscilloscope. Timing distributions of the sonoluminescence (SL) pulses from both emissions were compared and the distribution from Na-atom emission was found to be wider than that from the continuum emission. The results indicate the following conclusions. The Na-atom emission originates from those bubbles that have a wide radius distribution and low collapse temperature. The continuum emission originates from those bubbles that have a narrow radius distribution and high collapse temperature.

Estimation of the cavitation peak pressure using the Na D-line structure in the sonoluminescence spectra

The sonoluminescence (SL) spectra of an Ar-saturated NaCl solution in the region of the Na D line excited by ultrasound at a frequency of 22 and 44 kHz have been measured at a solution temperature within 5–20°C and the normal and elevated hydrostatic pressure. Based on an analysis of the obtained results in comparison to published data, it is established that variations in the intensity and structure of the Na D line in the SL spectra of NaCl solutions are related to changes in the intensity of the so-called red satellite. Using the measured red satellite intensity, the peak pressure in the cavitation bubbles was estimated at 800–1200 bar depending on the experimental conditions.

Experimental observation of the intense enhancement of metal sonoluminescence under pressure and temperature

The multibubble sonoluminescence spectra of argon-saturated aqueous salt solutions of alkaline and alkaline earth metals exhibit an intense enhancement of atomic emission with respect to continuum emission with an increase in the hydrostatic pressure and decrease in the solution temperature. It is suggested that ion reduction and metal atom excitation occur in the incandescent liquid layer formed at the liquid/bubble interface during a time interval that is sufficiently short for diffusion. The layer volume and, therefore, the number of “trapped” metal ions increases with an increase in the finite temperature in the cavitation bubble, which is caused by external factors.

Time-resolved spectra of single-bubble sonoluminescence in sulfuric acid with a streak camera

The time-resolved spectra of single-bubble sonoluminescence (SBSL) in sulfuric acid have been observed with a streak camera after a spectrograph. The spectral center evolves from infrared to ultraviolet gradually within a SBSL duration, which corresponds to an increase of temperature. The peak temperature within one sonoluminescence (SL) duration is 5-9 times higher than the average temperature based on the average spectrum in our experiment. Furthermore, the ratio of the peak temperature to average temperature increases with the increase of driving pressure. The SBSL flash dies out after a dramatic heating-up, and there is no cooling procedure observed at the time resolution of 110 SL duration, which is incompatible with the radius-related adiabatic heating model as the mechanism of SBSL.

Effect of argon on the multibubble sonoluminescence of cerium, terbium, and dysprosium trichlorides

The ultrasonic (20 kHz) multibubble sonoluminescence spectra of aqueous air- or argon-saturated solutions of CeCl3, TbCl3, and DyCl3 were obtained. Saturation with argon leads to the intensity redistribution in the spectrum of the continuum with an increase in its short-wavelength part and increases the intensity of the characteristic emission of Ce3+ and Tb3+ due to the enhancement of the sonophotoluminescence intensity, i.e., the re-emission of the absorbed part of the continuum by these ions. The Ce3+, Tb3+, and Dy3+ ions quench the OH* emission at 310 nm with a qualitative correlation between the degree of quenching and the standard redox potentials of the pairs LnIV/LnIII.

Sonoluminescence of Na Atom from NaCl Solutions Doped with Ethanol

Sonoluminescence spectra from argon-saturated NaCl solution were measured in the concentration range of 0.5-4 M at the frequency of 138 kHz. The line broadening of sodium atom emission was observed at various acoustic powers in the range from 1.8 to 16.2 W. The sodium D line showed a maximum intensity at a NaCl concentration of 2 M, which corresponded to the maximum production of OH radicals estimated by KI dosimetry. The effects of the addition of a small amount of ethanol on the line width and intensity were closely investigated at various acoustic powers. The sodium line width increases with ethanol concentration and also with power, whereas the line intensity is strongly quenched with increasing ethanol concentration. The results conclusively show that the sodium emission occurs in the gas phase within bubbles. The line broadening is due to interactions with high-pressure argon, and the maximum relative density of gas at bubble collapse was estimated to be 59.5 from the comparison with spectroscopic data. Further line broadening and quenching upon the addition of ethanol arise from collisions with gaseous products obtained from the decomposition of ethanol. The mechanism of sodium excitation is inferred to be as follows. Sodium ions enter bubbles as droplets, and salts are formed because of the high temperature within bubbles. Sodium atoms are generated by the dissociation of salts and then undergo electronic excitation by OH and H radicals.

The spectra of conical bubble sonoluminescence in 1,2-propanediol and glycol

A conical bubble straight tube apparatus was set up to study sonoluminescence. The spectra of conical bubble sonoluminescence for 1,2-propanediol and glycol were detected. The results show that the luminescence is intense, and the spectra consist of a broad background on which five clear sequences of Swan bands and three sequences of the B2Σ+ → X2Σ+ transition of CN are superimposed. A band assigned to the A2Δ → X2Π transition of CH was also measured and the vibrational and rotational structures of Swan bands could be resolved. The origin of the C*2 and C2H* is discussed. Finally, the achieved molecular vibrational temperature is estimated to be about 5400 ± 350 K.

Multibubble Sonoluminescence and Na Atom Emission in Sodium Dodecyl Sulfate Surfactant Solutions

Multibubble sonoluminescence spectra were measured in sodium dodecyl sulfate (SDS) solutions at the frequencies of 108 kHz and 1.0 MHz. At 108 kHz under a low power, the total sonoluminescence intensity is enhanced and reaches a maximum at 1 mM. At 108 kHz under a high power, the sonoluminescence intensity gradually decreases in the SDS concentration range of 0.1–100 mM, whereas at 1.0 MHz, the sonoluminescence intensity is rapidly quenched at a concentration of 1 mM and increases afterward. Na D-line peaks at 589 nm were observed at both frequencies for concentrations above 0.5 mM. Na atom emission is more prominent at 1.0 MHz than at 108 kHz. The frequency effect is discussed in terms of rectified diffusion including dynamic equilibrium isotherm for the surface excess of surfactant and the production of OH radicals.