Estimating the Radical Character of Surface Bound Hydroxyl Groups through an in-situ Ultra-Violet Photoelectron Spectroscopy study of UO2, U2O5 and UO3 exposed to H2O and H.

• Ultraviolet Photoelectron Spectroscopy (UPS) has been used to study the reactions of H2O and atomic hydrogen with UO2, U2O5 and UO3 at low temperatures and low dosages (below 50 Langmuir). The aim was to compare the formation and characteristics of surface hydroxyl species, either by dissociation of the water (surface hydration) or by reduction of the oxide by atomic hydrogen (surface hydrogenation). In addition, the charge state of the OH (neutral-radical or anion) was investigated. On UO2 and U2O5, water adsorbs molecularly and little surface OH was formed. Atomic hydrogen reduces U2O5, by forming OH species but reduction yield is low compared to that of UO3. On UO3 water only weakly adsorbs and already at -110°C it desorbs. Hydrogen reduces UO3, from U(VI) to U(V). Photochemical reduction of the oxides by water was observed for both UO3 and U2O5. The influence of the termination layer on the adsorption of water has been investigated for UO3. UPS has been used to characterize the chemisorbed H2O and OH via their molecular orbitals (MOs), for H2O 1b2, 3a1 and 1b1 for OH the 1and 1. The 3a1-1b1 binding energy difference was taken as measure for the bond strength. The 1 /1 intensity ratio was tentatively used to determine the charge state of the surface hydroxyl.

Ämnesord

NATURVETENSKAP  -- Kemi -- Oorganisk kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Inorganic Chemistry (hsv//eng)

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