Evidence for the emission of 'alkali-metal-noble-gas' van der Waals molecules from cavitation bubbles

Visible emission spectra in the vicinity of resonance lines of alkali metals were recorded from acoustically cavitating aqueous and 1-octanol solutions (acoustic frequency: 20 kHz; solutes: Ar (or Kr), NaCl, RbCl or rubidium 1-octanolate). The maximum intrabubble density deduced from line shift data was similar to5 +/- 0.7 x 10(26) m(-3), i.e. similar to 18 +/- 2 amagats. It is demonstrated that (i) the emission from alkali metals arose from the gas phase of bubbles, (ii) the blue satellite and line distortions were induced, respectively, by B(2)Sigma (+)-X(2)Sigma (+) and A(2)Pi -X(2)Sigma (+) transitions of 'alkali-metal/rare-gas' van der Waals molecules and (iii) excitation/de-excitation mechanisms are chemiluminescent in essence. (C) 2001 Elsevier Science B.V. All rights reserved.