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.