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 ∼5±0.7×1026 m−3, i.e. ∼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 B2Σ+–X2Σ+ and A2Π−X2Σ+ transitions of ‘alkali-metal/rare-gas’ van der Waals molecules and (iii) excitation/de-excitation mechanisms are chemiluminescent in essence.