Publication cost assisted by Hahn-Meitner-lnstitut fur KerntorschungThe reactions of fluorinated benzenes with hydrated electrons and hydroxyl radicals in aqueous solutions have been investigated by pulse radiolysis and 7-irradiation experiments. One fluoride ion per attacking eaq" is eliminated from the higher fluorinated compounds via a dissociative electron capture process.The yields of F_ ions are lower in the reaction of eaq~w ith mono-, o-di-, and p-difluorobenzene. The majority of electrons here interact with the aromatic ring, and the molecular anions thus formed are neutralized to yield fluorocyclohexadienyl radicals. The oxidation of fluorinated., benzenes by hydroxyl radicals occurs via addition of the OHto any of the six carbon atoms with alihost equal probability. If the attacked carbon atom carries a hydrogen atom a fluorohydroxycyclohexadienyl radical is produced. The addition to a carbon atom carrying a fluorine atom leads to the elimination of hydrogen fluoride. Rate constants have been determined for the reactions of the fluorinated benzenes with eaq-~a nd OHand for the reactions of transient species produced from these processes. Radicals and stable products have also been characterized by their optical absorption spectra. Mechanistic details of the reduction and oxidation reactions are discussed.

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Gas analytical microsystems such as the Karlsruhe micro nose (KAMINA) can be improved toward higher sensitivity when using SnO 2 nanoparticle thin films instead of well-established sputtered layers. For achieving long-term stability, such nanoparticles must be prevented from growing and agglomerating. A very promising approach is to coat SnO 2 nanoparticles with an open-pored SiO 2 shell, simply acting as a spacer, while preserving electrical contact between adjacent core particles. Such nanoparticulate thin films can easily be realized by the gas-phase Karlsruhe microwave plasma process (KMPP). This provides an all-in-one approach to synthesize particles with diameters less than 10 nm, to coat them in situ with a protective ultrathin SiO 2 shell in a downstream step and to finally deposit the core/shell particles solvent-free onto prefabricated micro devices.The present study focuses on the surface analytical characterization of 200 nm thin films consisting of SnO 2 core/SiO 2 shell nanoparticles with various shell designs. For this purpose, the SiO 2 shell thickness was systematically increased while keeping the SnO 2 core size constant. X-ray photoelectron spectroscopy (XPS) provides information concerning chemical binding states and shell thickness in a nondestructive manner. Angle-resolved XPS together with transmission electron microscopy (TEM) validate the achieved core/shell structure. In the case of the desired ultrathin SiO 2 shells, low-energy ion scattering (LEIS) is solely the suitable means to prove that Sn and Si are the constituents of the outermost monolayer of the spherical particles and it demonstrates the attainability of open-pored coatings.

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shaping prior to transformation. HETCOR spectra were acquired with sweep widths dictated by the appearance of the 13C and 'H spectra by using a 1024 X 512 data matrix and 128 increments in the first dimension. NOE-difference spectra were obtained with the decoupler gated off during acquisition time. A delay of 5 s was set between pulses. Spectra were obtained in an arrayed experiment with the decoupler set loo00 Hz off-resonance and then with the decoupler cycled over the multiplet structure of the desired proton for irradiation; the procedure of Kinns and Saunders'O was followed in this connection. The two resultant free induction decays (FIDs) were then subtracted and transformed. Acknowledgment. Financial support of our study by the Air Force Office of Scierltific Research, Air Force System Command (Grant AF'OSR-84-0085, to A.P.M.), the Robert A. Welch Foundation (Grant P-093, to W.B.S., Grant B-963, to A.P.M.), and the North Texas State University Faculty Research Committee (to A.P.M.) is gratefully acknowledged.Supplementary Material Available: The phase-sensitive, double quantum filtered COSY spectrum of 3 and the normal proton NMR spectrum of 3 with the NOE-difference spectra resulting from irradiation of the methyl group and irradiation of H-6 (4 pages). Ordering information is given on any current masthead page. (10) Kinns, M.; Saunders, J. K. M. J. Mugn. Reson. 1984, 56, 518. Isomerization and Thermolysis ofBis(9-borabicyclo[3.3.l]nonane)