Water vapour, sonoluminescence and sonochemistry

Sonoluminescence is the production of light from acoustically forced bubbles; sonochemistry is a related chemical processing technique. The two phenomena share a sensitive dependence on the liquid phase. The present work is an investigation of the fate and consequences of water vapour in the interior of strongly forced argon micro-bubbles. Due to the extreme nonlinearity of the volume oscillations, excess water vapour is trapped in the bubble during a rapid inertial collapse. Water vapour is prevented from exiting by relatively slow diffusion and non-equilibrium condensation at the bubble wall. By reducing the compression heating of the mixture and through primarily endothermic chemical reactions, the water vapour reduces the temperatures within the bubble significantly. The quantity and disposition of hydroxyl radicals produced within the bubble are studied in some detail, as this is of keen interest in sonochemistry. It was recently shown by Moss and co-workers that light emission from a sonoluminescence bubble depends sensitively on the water-vapour content. The quantity of trapped water vapour determined in the present analysis is in excellent agreement with the amount found by Moss and co-workers to match photon yields and pulse widths of recent experiments.