Browsing by Author "Prince, KC"

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    Adsorption structure of adenine on cerium oxide
    (Elsevier, 2020-11) Bercha, S; Bhasker-Ranganath, S; Zheng, X; Beranová, K; Vorokhta, M; Acres, RG; Skála, T; Matolín, V; Prince, KC; Xu, Y; Tsud, N
    The adsorption of adenine on the CeO2(1 1 1)/Cu(1 1 1) surface in vacuum was studied by photoelectron spectroscopy, resonant photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy, and the present work describes in detail the bonding of the molecule to the ordered stoichiometric cerium dioxide film. The experimental findings were supported by density functional theory (DFT + U) analysis of different adsorption geometries of adenine on CeO2(1 1 1). The phase with adenine lying flat on the surface dominates on CeO2(1 1 1) up to 0.1 monolayer (ML) of adenine coverage. The mobility of single molecules was apparently sufficiently high to allow diffusion and formation of chain structures, which were observed to be stable in the temperature range from 25 to 250 °C. Beyond 0.1 ML, adenine molecules adsorb predominantly in an upright orientation. This phase, stable up to 120 °C, is according to theory stabilised via N3/Ce4+ and N9H/O2–. It was further complemented by experimental findings demonstrating free N10H2 groups in adsorbed molecules. Thus, the saturation coverage of adenine on CeO2(1 1 1), 0.23 ML, is most likely characterised by a combination of parallel and upright bound molecules. © 2020 Elsevier B.V. All rights reserved.
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    Electronic structure and intramolecular interactions in three methoxyphenol isomers
    (AIP Publishing, 2018-10-07) Islam, SMA; Ganesan, A; Auchettl, R; Plekan, O; Acres, RG; Wang, F; Prince, KC
    Electronic structures and intramolecular interactions of three methoxyphenol positional isomers and their rotamers have been studied using core X-ray photoelectron spectroscopy and quantum mechanical calculations. The structural calculations are benchmarked against published calculations of enthalpy of formation and rotational constants, and published experimental data. The good agreement obtained confirms the accuracy of the results. A single rotamer of each isomer was then selected and the C 1s photoelectron spectra calculated and compared with experiment. Good agreement is obtained, and the calculations were extended to investigate the effects of conformation. For 3-methoxyphenol, the difference in the C 1s binding energy of the conformers is small, <0.15 eV. For 2-methoxyphenol, whose ground state includes an OH⋯OCH3 hydrogen bond, the higher energy rotamers show the largest shifts for the methyl carbon atom, whereas the ring carbon bonded to OH hardly shifts The theoretical differences in core level energies of the two rotamers of 4-MP are still smaller, <0.05 eV. By comparing calculations neglecting or including final state relaxation upon ionization, the relaxation energy of the phenyl carbons in all isomers is found to be ∼0.5 eV, while that of the methyl groups is ∼1.3 eV. © 2018 Author(s).