ESCA Studies of MoO ₂ and MoO ₃

Abstract

Abstract The metallic and the oxide states of Mo were analysed by ESCA. A pure Mo metal sample was ion‐etched and analysed. MoO 3 was formed by oxidation of Mo in oxygen. The four‐valent MoO 2 was prepared by oxidation of Mo in a H 2 O/H 2 gas mixture and by reduction of MoO 3 in hydrogen. The binding energies of the Mo 3d 5/2 and Mo 3d 3/2 signals representing the metallic state are 227.9 and 231.0 eV, respectively. The chemical shift of the Mo 3d signals recorded for MoO 3 is 4.8 eV. Each of the Mo 3d spin–orbit components recorded from MoO 2 consists of two peaks. The area ratio between the low and high intensity peaks are 1:2. The shift of the low intensity peak is 3.2 eV corresponding to the value expected by linear interpolation between the four and six valent states. The high intensity peak is positioned at 1.6 eV higher binding energy than the metallic state. It is suggested that the low energy shift is due to the structure of MoO 2 ; the MoMo distance in the structure is either 2.5 or 3.1 Å. Interaction between metal atoms gives a partly filled σ‐bond which screens the core electron and thereby the shift becomes lower. The chemical shift of the Mo 4+ signal recorded from molybdenum oxyhydroxide is 3.2 eV. It is the same as for the low intensity peak in MoO 2 representing the ionic character of the Mo atoms in the oxide.