Flannigan DJ, Suslick KS. Plasma formation and temperature measurement during single-bubble cavitation.
Nature 2005;
434:52-5. [PMID:
15744295 DOI:
10.1038/nature03361]
[Citation(s) in RCA: 274] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2004] [Accepted: 01/17/2005] [Indexed: 11/09/2022]
Abstract
Single-bubble sonoluminescence (SBSL) results from the extreme temperatures and pressures achieved during bubble compression; calculations have predicted the existence of a hot, optically opaque plasma core with consequent bremsstrahlung radiation. Recent controversial reports claim the observation of neutrons from deuterium-deuterium fusion during acoustic cavitation. However, there has been previously no strong experimental evidence for the existence of a plasma during single- or multi-bubble sonoluminescence. SBSL typically produces featureless emission spectra that reveal little about the intra-cavity physical conditions or chemical processes. Here we report observations of atomic (Ar) emission and extensive molecular (SO) and ionic (O2+) progressions in SBSL spectra from concentrated aqueous H2SO4 solutions. Both the Ar and SO emission permit spectroscopic temperature determinations, as accomplished for multi-bubble sonoluminescence with other emitters. The emissive excited states observed from both Ar and O2+ are inconsistent with any thermal process. The Ar excited states involved are extremely high in energy (>13 eV) and cannot be thermally populated at the measured Ar emission temperatures (4,000-15,000 K); the ionization energy of O2 is more than twice its bond dissociation energy, so O2+ likewise cannot be thermally produced. We therefore conclude that these emitting species must originate from collisions with high-energy electrons, ions or particles from a hot plasma core.
Collapse