1. Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA

Correspondence to: Kenneth S. Suslick¹ Correspondence and requests for materials should be addressed to K.S.S. (Email: ksuslick@uiuc.edu).

Abstract

Single-bubble sonoluminescence (SBSL^{1, 2, 3, 4, 5}) results from the extreme temperatures and pressures achieved during bubble compression; calculations have predicted^{6, 7} the existence of a hot, optically opaque plasma core⁸ with consequent bremsstrahlung radiation^{9, 10}. Recent controversial reports^{11, 12} claim the observation of neutrons from deuterium–deuterium fusion during acoustic cavitation^{11, 12}. 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 spectra¹³ 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^{14, 15, 16}. 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.

1. Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA

Correspondence to: Kenneth S. Suslick¹ Correspondence and requests for materials should be addressed to K.S.S. (Email: ksuslick@uiuc.edu).

MORE ARTICLES LIKE THIS

These links to content published by NPG are automatically generated.