Sorption of uranyl cations on a rutile (001) single crystal monitored by surface second-harmonic generation.

The rotational anisotropy of second-harmonic generation at the surface of a (001) single-crystal rutile is obtained in the presence of uranyl cations sorbed at the surface from acidic solutions at various concentrations. Surface second-harmonic generation appears to be sensitive to the presence of uranyl cations on the rutile samples. Evolution of the anisotropy pattern with initial uranyl concentration is analyzed through a phenomenological model. The elements obtained for the nonlinear susceptibility tensor Chi(2) for each sample significantly constrain the geometry of the possible sorption complexes between uranyl cations and rutile and lead to the proposition of two sorption sites involving different oxygen atoms of the rutile surface.