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 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.

Articles you may be interested inMolecular and atomic emission during single-bubble cavitation in concentrated sulfuric acid ARLO 6, 157 (2005); 10.1121/1.1897810Conditions during multi-bubble cavitation AIP Conf.Abstract. Intense Na* emission in sulfuric acid was observed in different spatial locations from blue emission. The color change from blue to orange observed along the streamer in the filamentous structure of a bubble cloud even with the naked eye. The Na* emission seemed to be generated after bubble coalescing. The intensity of Na* emission increased at lower frequency, where bubbles may grow more easily to lead more energetic surface oscillations.

Articles you may be interested inOn a shape of alkali-metal lines in sonoluminescence spectra AIP Conf.Abstract. Sonoluminescence spectrum from alkali-metal salt solutions contains continuum component and line emission from alkali-metal atoms. We measured sonoluminescence from argon-saturated 2M KCl solutions at frequencies of 28 kHz, 48 kHz, 115 kHz, 510 kHz, and 1MHz at various powers. Effect of ethanol on the linewidth and intensity was studied at 115 kHz. The K-atom line showed asymmetric broadening toward the red in all the experimental conditions. Adding 1mM ethanol caused further line broadening and quenching at 115 kHz. These results indicated the K-atom emission occurs in gas phase inside bubbles and the line broadening is resulted from interaction of K atom with argon and molecules decomposed from ethanol.Frequency dependence of K-atom linewidth and intensity were investigated. The linewidth decreased with increasing frequency, and the intensity took maximum value at 115 kH. Discussion was made in terms of foreign gases interacting with K atoms.