With this study on KDP, we present an interface atomic structure determination of a crystal in contact with its growth solution. Using x-ray diffraction at a third-generation synchrotron radiation source, the structure of both the ͕101͖ and ͕100͖ faces has been determined. We found that the ͕101͖ faces are terminated by a layer of K 1 ions and not by H 2 PO 2 4 groups, resolving a long-standing issue that could not be predicted by theory. This result leads to an atomic-scale explanation of the influence of metal impurities on the macroscopic growth morphology. [S0031-9007(98)

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We have investigated the vacuum ultra-violet photodissociation of molecular O2 physisorbed on graphite using synchrotron radiation with photon energies in the range 13-35 eV. The yield of desorbed O+ ions shows a threshold at approximately 19.5 eV and resonances at 24.5 eV and 28.5 eV, contrasting strongly with the gas phase photodissociation cross section. The principal mechanism of O+ production appears to be dipolar dissociation driven by photoelectrons generated in the substrate. An enhancement in the detection efficiency of low-energy ions, compared with previous measurements, has identified an additional dissociation mechanism leading to the desorption of O- ions. Specifically, the results support a channel for low-energy O- desorption, attributed to the dissociative attachment of photoelectrons, again generated in the graphite substrate, to the physisorbed O2 molecules.

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