Photochemistry of the uranyl ion in solution

146 Polychloriuated biphenyl isomers: photolysis in aqueous systems

DEMETRIOS

ZADELIS

and

MILAGROS

S. SIMMONS

Environmental Chemistry Laboratory, Department of Environmental and IndustrialHealth, 2530 SPH Z, The Universiv of Michigan, Ann Arbor, MI 48109 (U.S.A.)

The photochemical decomposition of isomers of chlorinated biphenyls in aqueous media was studied. The irradiation was conducted at the 300 nm maximum using a Rayonnet photochemical reactor. The rate of photodecomposition and quantum yield for each isomer were calculated. A correlation of photolytic half-lives with physicochemical properties of the isomers is presented. Photoproducts were identified using gas chromatography with mass spectrometry. The results of studies on the effects of the variation in light sources and the presence of humic acid and particulates in aqueous media are presented.

Static fluorescence quenching of aromatic hydrocarbons by the uranyl ion

S. J. FORMOSINHO,

M. G. MIGUEL

and

A. C. CARDOSO

Chemistry Department, University of Coimbra, 3000 Coimbra (Portugal)

Fluorescence quenching rate constants for aromatic hydrocarbons quenched by the uranyl ion were measured in ethanol. Static quenching via the formation of a non-emissive complex already present in the ground state was observed. The dependence of the equilibrium constants on temperature shows a positive entropy variation that is responsible for the uranyl ion-hydrocarbon association. In nonpolar solvents no static quenching was observed,

Photochemistry of the uranyl ion in solution

M. ARVIS,

N. KELLER,

G. FOLCHER

and

B. HICKEL

D6partemen t de Physicochimie, Centre d’Etudes Nuclkaires de Sacluy, 9I I 91 Gif sur Yvette CWex (France)

There is a growing interest in the use of uranyl salts for solar energy because the excited state has a very high oxidation potential. We studied the reactions of this state by flash photolysis and time-resolved fluorescence.

147 In aqueous perchloric acid solutions the lifetime of the excited state observed by both methods increased with the acid concentration. In the presence of nitric acid, quenching of fluorescence occurred and the transient formation of the N03* radical, identified from its absorption spectrum, was observed. The effect of acidity and NO, ion concentration on the kinetics and mechanism of NO3 - formation are discussed_

Photochemistry of c~-chlorodimethylsulphoxide-bis(etbylenedi) and cis-bis(dimethylsulphoxide)-bis(ethylenediamine)Cr(III) complexes

CLAUDIO

BIFANO

Facuitad de Ciencias, Universidad

Central de Venezuela, Apto. 3895,

Caracas (Venezuela)

The photochemical and thermal behaviours of cis-chlorodimethylsulphoxidebis(ethylenediamine)Cr(III) and cis-bis(dimethylsulphoxide)-bis(ethylenediamine)Cr(III) complexes were studied. The complexes were irradiated with a 1000 W lamp at the wavelength corresponding to the first d-d transition at a temperature of 4 - 5 “C. The photoproducts were separated by ion exchange chromatography and were characterized by their spectrochemical parameters and the Cr:ligand ratios. The thermal study was carried out similarly. The results are discussed in terms of proposed models.

Photochemistry of Cr(NCS),(bipy)-

HEINZ

J. KRENTZIEN

Facuhd

de Ciencias. Unirersidad

and Cr(NCS)&hen)-

Central de Venezuela, Apto. 3895, Caracas (Venezuela)

The photochemical and thermal behaviours of the Cr(NCS),(bipy)- and Cr(NCS)&hen)complexes were studied. The complexes were irradiated at their first d-d transition band at 5 “C. The quantum yields for the photochemical path are 0.02 and 0.05 respectively. These anomalously low values are discussed in terms of the n bonding model proposed by Gray et al.