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High-accuracy approximations of the bound-state energies of the Hulthen potential are obtained by means of algebraic perturbation calculations which are based upon the dynamical-group structure SO(2, 1).

The ESR spectrum of X-irradiated carbonated apatites synthesized at low temperature was studied as a function of their carbonate content. Using 13C-enriched samples, four different carbonate-derived radicals and a surface O- ion could be identified. Isotropic CO3- and CO2- ions are present at a B site in the apatite lattice, and anisotropic CO3- and CO2- radicals are located at the surface of the crystallites. Only the isotropic ESR signals increase with increasing carbonate content. The anisotropic signal ascribed to a surface CO2- radical is mainly responsible for the so-called asymmetric ESR signal near g = 2. It is argued that this surface signal may still be composite and caused by several very similar CO2- ions. The consequences for phenomenological ESR studies of calcified tissues are discussed.

Beta-D-fructose single crystals were in situ X-irradiated at 80 K and measured using electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR) and ENDOR-induced EPR (EIE) techniques at Q-band (34 GHz) microwave frequencies. The measurements revealed the presence of at least four carbon-centered radicals stable at 80 K. By means of ENDOR angular variations in the three principal crystallographic planes, six proton hyperfine coupling tensors could be determined and were assigned to four different radicals by the aid of EIE. Two of the radicals exhibit only beta-proton hyperfine couplings and reveal almost identical EIE spectra. For the other two radicals, the major hyperfine splitting originates from a single alpha-proton hyperfine coupling and their EIE spectra were also quite similar. The similarity of the EIE spectra and hyperfine tensors led to the assumption that there are only two essentially different radical structures. The radical exhibiting only beta-proton hyperfine couplings was assigned to a C3 centered radical arising from H3 abstraction and the other radical suggested to be an open-ring species with a disrupted C2-C3 bond and a double C2-O2 bond. A possible formation mechanism for the latter open-ring radical is presented. By means of cluster density functional theory (DFT) calculations, the structures of the two radicals were determined and a fairly good agreement between the calculated and experimental hyperfine tensors was found.

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deviations at intermediate [I-]. Instead they are distributed randomly around the curve which can be calculated applying (3b) (which gives about the same value for k l ) . IVe conclude that with a probability of more than 99.5% (3b) represents the actual mechanism of the main paths of the reaction, and (4) as well as (3a), (3d), and (3e) can be ruled out The standard deviation, s, calculated from (3b) is 6 97c, which is not far from the predicted experimental error However minor paths of order zero and three with respect to H + are not ruled out and actually are strongly suggested by the results. Using the weight equationsI7 we have calculated the standard deviations of the parameters of (3b) which are given in the text.An analogous treatment was applied to the data of Table I1 with generally similar results. In particular (3b) is confirmed to be significantly superior to (3a) and (3d) and (3e) give a negative meaningless value for the rate constant corresponding to ( p l y ) = (1>2). KO definite conclusion can be reached from these runs about the relative merits of (3b) and (4) due to the narrow range of [I-] The purpose of these runs was in fact to rule out, even a t I = 3.00 M, the contribution of a path first order with respect to H + and second order with respect to I-. This contribution can be ruled out with a probability of more than Y7.5YO ( x * (~, , ) = 17.6 and x2(sa) = 30.1, for 16 degrees of freedom x 2 ( 9 o ? % ) = 23.5 and ~~( 9 7 . 5 % ) = 28.8).Dodecacarbonyltriruthcnium, pentacarbonylruthenium, and tris(acetylacetonato)ruthenium(III) were found to promote the homogeneous reduction of nitrobenzene to aniline by carbon monoxide and hydrogen in good yields and conversions. At CO:HZ ratios higher than 1, diphenylurea is also a product of the reaction ancl its yields increase gradually with the CO:H? ratio. Product balance a t very high CO:H? ratios s h o m that carbon monoxide participates in the reduction and thus the stoichiometry of the reaction is probably C6H5N02 f 2CO + HZ -f C G H~S H~ + 2C02. X reaction mechanism is proposed in which a phenylnitrene intermediate stabilized by bonding t o ruthenium in a binuclear complex undergoes either hydrogenolysis to give aniline or CO insertion and hydrogenolysis to give 2,2'-diphenylurea. Pentacarbonyliron is considerably less active than ruthenium in promoting the reduction of nitrobenzene; a possible interpretation of this fact is given.

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