Sonoluminescence from Nonaqueous Liquids: Emission from Small Molecules

Sonoluminescence spectra from nonaqueous liquids under a variety of gases are presented. Ultrasonic irradiation of alkanes under Ar leads to emission from C2, C2H, and CH. When nitrogen is present, emission is seen from CN. When oxygen is present, emission from COz, CH, and OH is observed. Ultrasonic irradiation of tetrachloroethylene or CCI4 leads to emission from CI2. The intensity of sonoluminescence decreases as the liquid vapor pressure increases. The properties of the dissolved gas also influence the sonoluminescence observed. Sonoluminescence is caused by chemical reactions of high energy species formed during cavitational collapse. It is a form of chemiluminescence. The principal source of sonoluminescence is not blackbody radiation or electrical discharge. Ultrasonic irradiation of liquids can produce light. This phenomenon, known as sonoluminescence (SL), was first observed from water in 1934 by Frenzel and Schultesl and from organic liquids in 1937 by Chambers.* Although sonoluminescence from aqueous solutions has been studied in some detai1,3,4 little work on sonoluminescence from nonaaueous liauids has been reDorted. and Leeman have recently proposed a shock-wave model? where SL is caused by a shock-wave from the collapsing bubble wall. In the hot-spot chemiluminescence m ~ d e l , ! ~ J ~ which is the best (1) Frenzel, H.; Schultes, H. 2. Phys. Chem. 1934, 276, 421. (2) Chambers. L. A. J . Chem. Phvs. 1937. 5. 290. We present here sonoluminescence spectra from several nonaqueous liquids in the presence of various gases. We conclude that sonoluminescence from organic liquids is caused by emission from small free radicals and molecules, such as C2, CN, C02, and Cl,. A preliminary reports of this work has been published. There has been some dispute over the mechanism of sonolumine~cence.~ All of the theories of SL invoke acoustic cavitation6 (the formation, growth, and implosive collapse of bubbles in solution), as the source of the phenomenon. Noltink and Neppiras proposed SL was from blackbody emission' of the heated cavity. Electrical discharge8 inside the bubble has been proposed several (3) Verrall, R. E.; Sehgal, C. M. Ultrasound: its Chemical, Physical, and Biological Effects; Suslick, K. S., Ed.; VCH Publishers: New York, 1988. (4) Walton, A. J.; Reynolds, G. T. Adu. Phys. 1984, 33, 595. (5) Suslick, K. S.; Flint, E. B. Nature (London) 1987, 330, 553. (6) (a) Atchley, A. A.; Crum, L. A. In Ultrasound its Chemical, Physical, and Biological Effects; Suslick, K. S. , Ed.; VCH Publishers: New York, 1988. (b) Neppiras, E. A. Phys. Rep. 1980, 61, 159. (7) Noltink, B. E.; Neppiras, E. A. Proc. Phys. SOC. 1950, 638 , 674. (8) (a) Harvey, E. N. J. Am. Chem. SOC. 1939,61,2392. (b) Frenkel, Ya. I . Russ. J . Phys. Chem. 1940, 14, 305. (c) Degrois, M.; Baldo, P. Ultrasonics 1974, 14, 25. (d) Margulis, M. A. Ultrasonics 1985, 23, 157. (9) Vaughan, P. W.; Leeman, S. Ultrason. Int . Con$ (Proc.) 1987, 297. (10) Fitzgerald, M. E.; Griffing, V.; Sullivan, J . J . Chem. Phys. 1956, 25, 976 times as the source of SL, most recently by M a r g ~ l i i . ~ ~ Vaughan (1 1 ) (a) Suslick, K. S.; Hammerton, D. A,; Cline, R. E. J. Am. Chem. SOC. 1986, 108, 5641. (b) Suslick, K. S.; Hammerton, D. A,; Cline, R. E. IEEE Trans. Ultrason., Ferroelectr., Freq Control 1986, UFFC-33, 143. (c) Suslick, K. S.; Cline, R. E.; Hammerton, D. A. IEEE Ultrason. Symp. 1985, 1 1 16. *Author to whom correspondence should be addressed. 0002-7863/89/ 15 11-6987$01.50/0