Abstract
The shape of the temperature dependences of the lifetime (τ) of electronically excited uranyl ion (UO22+)*, measured on warming from 77 K of UO2SO4 solutions in H2SO4 + H2O, differs from that measured in D2SO4 + D2O. The lifetime in glassy D2SO4 is shorter than in the polycrystalline sample, whereas in frozen H2SO4 solutions the pattern is opposite. The isotope effect is due both to different course of phase transitions in H2SO4 and D2SO4 solutions and to the fact that the probability of nonradiating deactivation of (UO22+)* adsorbed on the surface of D2SO4·4H2O crystal hydrate is appreciably lower than that of (UO22+)* adsorbed on the surface of H2SO4·4H2O and H2SO4·6.5H2O crystal hydrates. We suggest that the increase in τ due to adsorption appreciably exceeds the concentration quenching of excited uranyl ions in the course of crystallization of deuterated sulfuric acid.
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