parabolas in Figure 7 and are listed in Table I. As can be seen from this table, the good agreement between the equilibrium constants determined separately by the computer simulation and those determined by the experimental approach stresses the validity of mechanism 1. This fact moreover supports the coordinate adsorption of the meta1,ions reported by McBride.13 Plots of e,'" and PTiP;t vs. the hydrolysis constant of M2+, Kh, are shown in Figure 8, showing the correlation between them. This correlation reveals that the surface complexes, -A10M(H20),,+ and -A10MOH(H20),2, result from the hydrolysis of the metal ion adsorbed, Le., surface hydrolysis.The applicability of the model proposed to the similar experimental results reported by Hohl and Stumm, where the concentration of metal ion is fairly dilute compared with the present experimental conditions,s was examined, and their results could be interpreted by mechanism I. On the other hand, Davis and Leckie have also explained by their model the results reported by Hohl and Stumm.]] In conclusion, both models can be applied to experimental results obtained at fairly dilute concentrations In aqueous y-A1203 suspensions containing divalent metal ions Cuz+, Mn2+, Zn2+, Co2+, and Pb2+, double relaxations were observed by using the pressure-jump technique with electric conductivity detection. For all y-A1203-metal ion systems, both fast and slow relaxation times decrease with the concentration of metal ions and increase with that of protons. From the kinetic results obtained, the fast and slow relaxations were attributed to simultaneous adsorption-desorption of metal ions on surface sites of the largest fraction and on the remaining sites existing on a y-A120, surfaae, respectively. It was found that the order of adsorption rate constants of metal ions corresponds to that of the rate constants for the release of a water molecule from the hydrated metal ions in homogeneous metal complex systems.

23The main photochemical consequence of these conclusions is obviously that small structural modifications of such compounds may yield very large changes in the quantum yields of chemical reactions occurring from one specific triplet geometry. triplet energies of the planar and perpendicular geometries, may yield a drastic modification of this equilibrium.The resulting changes in the percentage of planar and perpendicular triplets can easily be detected since the intrinsic ---properties of these species, e.g., their deactivation rate constantsThe relative amount of the planar and perpendicular triplets is also greatly modified by changing the a-naphthyl group to other aromatics and it seems that the lower the triplet energy of the Registry No.The adsorption isotherms and pH dependences of the adsorption of the divalent metal ions CuZt, MnZt, ZnZt, Co2+, and Pb2+ on a y-A1203 surface were measured, and it was found that these metal ions are specifically adsorbed. The experimental results obtained were explained on the basis of the model of adsorption-desorption by coordinate binding and the intrinsic equilibrium constants for each steps were determined. In the equilibrium analysis, a surface potential created by both metal ions and protons adsorbed on the same surface plane was newly introduced. The equilibrium constants for metal ion adsorption With release of a proton are in the same order as the hydrolysis constants of metal ions in homogeneous aqueous solution, namely Cu > Pb > Zn > Co > Mn.

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Double relaxations were found in aqueous -1203 suspensions containing mono-and divalent phosphate ions by using the pressure-jump technique with electric conductivity detection. The relaxations were observed over the range of pH 5-8.5, where the major phosphate adsorption site is the protonated surface hydroxyl group. The fast relaxation time decreases with pH, while the slow one increases. Taking into account the surface potential calculated from the ("-potential on the basis of the Davis, James, and Leckie model, we can attribute the fast and slow relaxations to the adsorption-desorption reactions of diand monovalent phosphate ions on the protonated surface hydroxyl group, respectively. The intrinsic values of the adsorption and desorption rate constants for the monovalent phosphate were determined to be V* = 4.1 X 105 mol"1 dm3 4s"1 and k^'Dt = 2.3 s"1, and those for the divalent phosphate were k2int = 1.1 X 107 8mol"1 dm3 s'1 and k_2int = 2.7 s'1, respectively, at / = 1.5 X 10"2 and 25 °C. mechanism.

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