The Origin of Isotope Effects in Sonoluminescence Spectra of Heavy and Light Water

Abstract

Die Isotopeneffekte in den Sonolumineszenzspektren von leichtem und schwerem Wasser unter Ultraschallbestrahlung wurden gemessen. Die Ergebnisse weisen auf die Bildung eines Nichtgleichgewichtsplasmas innerhalb der kollabierenden Kavitationsblasen hin. Das Bild zeigt die aktiven Kavitationszonen in Wasser bei 204 kHz.

A power-triggered preparation strategy of nano-structured inorganics: sonosynthesis

“…[16] To date, several competing theories have been postulated to explain the chemical effects created by ultrasound irradiation, but most of them are completely discarded as a valid mechanism of sonoluminescence and sonochemistry. [39][40] Since the acoustic cavitation accounts for the transient characteristic conditions, the hotspot theory has become more generally accepted, where it highlights that the extreme conditions from the localized hotspots will form a few active species for the follow-up sonochemistry. In a system, the bulk of liquid has no direct sonochemical events, but the compressional heat released from collapsing bubbles generates enough high temperatures effectively and locally inducing the dissociation of chemical bonds, and the induced radicals may diffuse into the liquid prior to the further reactions.…”

“…As a powerful tool to understand the origin of the drastic conditions created by acoustic cavitation, the analysis of sonoluminescence spectra from water under power ultrasound reveals the overpopulation of OH(A 2 Σ + ) vibrational levels, indicating the formation of nonequilibrium plasma inside the cavitation bubbles. [40] The non-equilibrium plasma is the major state of gas inside violently collapsing cavitation bubbles. Based on a two-site model for the sonochemical regions, most of the radical production is thought to occur in the interior vapor phase when the liquid layer immediately surrounding the cavitation bubbles bursts into the bubbles upon the cavitation collapse.…”

Radical production inside an acoustically driven microbubble

“…We assume that the bubble contains a perfect gas with a spatially uniform temperature and pressure, i.e. low Mach numbers, and we neglect the formation of a non-thermal plasma inside the bubble at collapse [36][37][38]. We also assume spherical symmetry and shape stability, thus restricting our study to a range of parameters where these assumptions are reasonable [48,49].…”

“…In a strict sense, talking about ''the temperature'' inside the bubble at collapse may also be misleading, since thermal equilibrium is not reached and a non-thermal plasma is formed, where the electron temperature is different from the vibrational temperature (e.g. of OH) and from the gas temperature [36][37][38].…”