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Spectroscopy and photochemistry of the uranyl(VI)
Albano Univ Ctr, Inst Phys, Rollagstullbacken 21, S-10406 Stockholm, Sweden..
Univ Sci Technologies Lille, CNRS, Lab PhLAM, UMR8523, F-59655 Villeneuve Dascq, France..
Albano Univ Ctr, Inst Phys, Rollagstullbacken 21, S-10406 Stockholm, Sweden..
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry (closed 20110630). Univ Sci Technologies Lille, CNRS, Lab PhLAM, UMR8523, F-59655 Villeneuve Dascq, France..
2006 (English)In: RECENT PROGRESS IN COMPUTATIONAL SCIENCES AND ENGINEERING, VOLS 7A AND 7B / [ed] Simos, T Maroulis, G, VSP BV-C/O BRILL ACAD PUBL , 2006, p. 979-+Conference paper, Published paper (Refereed)
Abstract [en]

The U - O bond in the uranyl(VI) ion is in general considered to be kinetically inert in thermal reactions, such as isotope exchange reactions. However, a fast isotope exchange can take place in photochemical reactions under UV irradiation as exemplified by the reaction UO22++H-2*O -> U*O-2(2+) + H2O (1). *O denotes oxygen enriched in the isotope 170 or O-18. Under daylight, no exchange takes place, or the rate of exchange is very slow. This suggests that the reaction involves the excited-states of the uranyl(VI). In order to explore the mechanism of exchange it is necessary to have information on the chemistry of the excited states and their electronic structure. it seems reasonable to assume that "yl"-isotope exchange is related to the U - O-yl, stretching modes and following the work of Pierloot and van Besien(1) we have therefore studied the a(g)- and a(u)-modes of the U-O-yl bond using different methods such as CASPT(2,3), standard MRCI calculations, TD-DFT 133LYP(4,5) and DFT-MRCI6. These benchmark calculations are used to provide a computational cost effective model for the study of the photochemistry of actinide compounds. We suggest that the first step in the "yl" exchange involves transfer of a proton from a coordinated water molecule to the "yl" oxygen ions. We have investigated this reaction for a model system involving the uranyl ion and a single water-molecule. We have followed the reaction profile in the ground state, in the luminescent state (3)Delta(g) (sigma u (1)f(delta)(1)) and in a higher lying excited state (3)Gamma(g), which corresponds to the excitation from the highest occupied pi(u), orbitals to the f(delta) orbital. This results in a distorted uranyl structure and the 3 F. state seems to be a good candidate for the photochemically "active" state where the increase of the U-O-yl, bond-length modifies the electronic density in the uranyl ion, so that the distant "yl" oxygen become more negatively charged and a stronger proton acceptor.

Place, publisher, year, edition, pages
VSP BV-C/O BRILL ACAD PUBL , 2006. p. 979-+
Series
LECTURE SERIES ON COMPUTER AND COMPUTATIONAL SCIENCES, ISSN 1573-4196 ; 7A-B
Keywords [en]
actinides, DFT, DFT-MRCI, TD-DFT, proton-exchange, uranyl, photochemistry, excited-states
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-242444ISI: 000254378800229ISBN: 978-90-04-15542-8 (print)OAI: oai:DiVA.org:kth-242444DiVA, id: diva2:1287417
Conference
International Conference on Computational Methods in Science and Engineering, OCT 27-NOV 01, 2006, Chania, GREECE
Note

QC 20190211

Available from: 2019-02-11 Created: 2019-02-11 Last updated: 2019-02-11Bibliographically approved

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