Cavitation thermometry using molecular and continuum sonoluminescence

Abstract

The focus of this study is the use of molecular and continuum emission spectra from multiple bubble (MB) and single bubble (SB) sonoluminescence (SL) as a probe of bubble temperature during cavitational collapse. It is proposed that molecular and continuum SL arise from different chemical pathways, which occur during discrete intervals along the cavitational collapse timeline, and yield different cavitation temperatures. A coupled dynamics/chemical kinetic model of cavitational collapse is developed, and used to explore a variety of proposed molecular SL chemiluminescent reaction mechanisms for the C2 (d→a), CN(B→X), and OH(A→X) emissions. This emission is broadly characterized as originating from reactions involving singly- or multiply bonded molecular precursors with corresponding effective emission temperature ranges of approximately 3000–8000 K and 8000–25 000 K, respectively. The continuum is similar for both SBSL and MBSL; based on the confined electron SL emission model, it is characterized by a temperature range of approximately 20 000–100 000 K. It is concluded that both SBSL and MBSL are consistent with an adiabatic compressional heating description of bubble collapse, and the observed differences in their SL spectra are attributed to the broad initial size distribution of cavitating bubbles for MBSL.