High frequency sonoluminescence in sulphuric acid and phosphoric acid

Multibubblesonoluminescence (MBSL) emission spectra at different forcing frequencies ( 20, 580, 850 KHz and 1.1 MHz) in Sulphuric acid and Phosphoric acid, under different noble gases atmosphere ( Ar, Xe and He) have been investigated. Using lower frequency we observed the presence of new emissions lines which may indicate the formation of ionized species with very high energy level inside the bubbles. Since it was recently demonstrated that MBSL at higher frequencies evidences the formation of line emission from OH radicals due to non-thermal mechanism, supporting also the calculation which suggest that highest temperature can be achieved at the bubbles core, we subjected these inorganic acids, saturated with noble gases, to high power, high frequency and also focused ultrasonic fields. The emission spectra revealed that the presence of emission lines is strongly reduced, probably due to the more symmetric bubbles collapse at these frequencies, due also to higher viscosity of these liquids respect to the water. On the other hand the contribution in the far UV region confirms the presence of ionized species due non thermal plasma formation although no significant differences in the emission spectra between focused and non-focused ultrasonic fields have been observed.