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Science 27 July 1979:
Vol. 205. no. 4404, pp. 390 - 394
DOI: 10.1126/science.205.4404.390
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Articles

Isotope Selectivity of Infrared Laser-Driven Unimolecular Dissociation of a Volatile Uranyl Compound

D. M. COX 1, R. B. HALL 1, J. A. HORSLEY 1, G. M. KRAMER 1, P. RABINOWITZ 1, and A. KALDOR 1

1 Exxon Research and Engineering Company, Corporate Research Laboratories, Linden, New Jersey 07036

Isotope-selective photodissociation of the volatile complex uranyl hexafluoroacetylacetonate · tetrahydrofuran [UO2(hfacac)2 · THF] has been achieved with both a continuous-wave and a pulsed carbon dioxide laser. The photodissociation was carried out in a low-density molecular beam under collisionless conditions. Transitions of the laser are in resonance with the asymmetric O-U-O stretch of the uranyl moiety, a vibrational mode whose frequency is sensitive to the masses of the uranium and oxygen isotopes. Unimolecular dissociation is observed mass spectrometrically at an extremely low energy fluence, with no evidence of an energy fluence or intensity threshold. The dissociation yield increases nearly linearly with increasing energy fluence. At constant fluence the dissociation yield is independent of contact time between the radiation field and the molecule, indicating that the decomposition is driven by laser energy fluence and not laser intensity. The oxygen and uranium isotope selectivities measured in these experiments are nearly those predicted by the ratio of the linear absorption cross sections for the respective isotopes. Thus, essentially complete selectivity is observed for oxygen isotopes, while a selectivity of only about 1.25 is measured for the uranium isotopes. A model presented to describe these results is based on rapid intramolecular vibrational energy flow from the pumped mode into a limited number of closely coupled modes.

Submitted on February 28, 1979
Revised on May 23, 1979


THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Actinide Organometallic Chemistry.
T. J. Marks (1982)
Science 217, 989-997
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Science. ISSN 0036-8075 (print), 1095-9203 (online)