Spectrophotometric, titrimetric, electron spin resonance and 77Se nuclear magnetic resonance studies made on the alkaline selenide, selenium electrolyte showed that soluble selenium species existed in four oxidation states, none of the species was a radical, and the mean state of oxidation of the Se-saturated solution was equivalent to Se3.82. It was concluded that the species were Sen2- with n = 1, 2, 3 and 4, or their protonated forms. On the basis of the Nernst equation, we analysed independently (A) the titration Eredox against the mean state of oxidation of the solution and (B) the absorption spectra of solutions with different mean states of oxidation. Thus formal redox potentials E′ were determined as E′12 = -0.935, E′13 = -0.931 and E′14 = -0.914 V against s.c.e. for the couples Se2-, Se22-; Se2-, Se32-; and Se2-, Se42- respectively in 1 mol dm-3 KOH supporting electrolyte at 304 K. It followed that E′23 = -0.919 for Se32-,Se32- and E′34 = -0.778 for Se32-,Se42-. The concentration of each species at each redox potential and the absorption spectrum of each distinct oxidation state were found. Excellent fits and agreement between the two analyses were observed. Ultraviolet absorption spectra showed that the reduced ion was approximately 50% protonated in 1 mol dm-3 KOH supporting electrolyte.

Photocatalytic solar water splitting has the potential to become a low‐carbon source of hydrogen fuel over the coming decades if the issue of low visible light absorption can be addressed without sacrificing chemical stability. We report on an investigation into the potential of the Bi–W‐oxides, Bi2WO6 and Bi6WO12, as visible light photocatalysts. X‐ray diffraction and Raman spectroscopy have been used to assess the structure of the oxides, whilst UV–vis diffuse reflectance spectroscopy analysed with the Kubelka–Munk function has been used to identify their optical band gaps. It has been revealed that Bi6WO12 shows significantly higher optical absorption in the region above 440 nm than either Bi2O3 or WO3, raising the possibility of enhanced photocatalytic activity under solar illumination. Bi2WO6 has a marginally lower band gap at 2.59 eV than Bi2O3 or WO3 but the results reported herein raise doubts concerning its chemical stability under aqueous, illuminated conditions for protracted periods of time. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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The occurrence of ionized states in a molecular crystal such as naphthalene is discussed. Such states are estimated to lie a t energy levels accessible with visible and ultraviolet light. The transition probability to the state in which the electron is transferred to the nearest neighbour corresponds to fZThe importance of such states to crystal spectroscopy and to photo-and semi-conduction is considered.PHOTOCONDUCTION in crystals such as anthracene in dry air is predominantly a surface effect, but there has also been observed2 a small but definite bulk photoconductivity which is possibly an intrinsic property of the crystal. The theory of light absorption by such crystals has been based upon neutral excitation waves, in which the excitation is transferred from molecule to molecule throughout the crystal and has successfully explained many dominant features of the crystal absorption spectrum at the longer wavelengths, e.g., the relation to the single-molecule spectrum, the Davydov splitting, and the intensity of absorption. Since a neutral excitation wave is not associated with conductivity, we must now ask what is the possibility of obtaining ionized excited electronic states as a result of light absorption. Extrinsic, surface, and secondary effects are neglected at present. Certain of the results have been summarized in a preliminary r e p ~r t . ~ Excited electronic states of a molecular crystal can be described, on the usual