Structure of ethane monolayers adsorbed on MgO(100): Experiments and calculations

Thermodynamic Investigation of Thin Films of Ethane Adsorbed on Magnesium Oxide

“…The peaks without the indication of an error are more ambiguous: [ ) neutron diffraction; 20 ) ) LEED. 21,22 (C-C molecular axis parallel to the MgO surface). The marked statistical improvement in the present diffraction data is most likely due to the chemical purity, size uniformity, and mean size of the MgO particles as was noted in our earlier findings 3,28 as well as the high flux and appropriately matched resolution of the instrument used here (OSIRIS).…”

Structure of the neopentane monolayer adsorbed on MgO(001): experiments and calculations

“…Such a misfit is not surprising since the nearest neighbor distance between two neopentane molecules in the bulk is equal to 6.21 A. According to the selection rule of Bragg diffraction applied to this c(2 · 4) unit cell, the ðhkÞ reflections with ðh þ kÞ odd are extinguished, consequently, the unique reflections not extinct are (02) and (11). Note that, considering that the orientational order-disorder transition of the neopentane bulk (3D) takes place at 140 K, we have considered in the fit two molecules rotating freely around their equilibrium position.…”

“…The primitive cell of the former monolayer structure (S 1 ) contains one molecule, whereas the latter structure (S 2 ) corresponds to two inequivalent molecules per primitive cell. In the minimization procedure, it is assumed that equivalent molecules pertaining to other cells move in the same way as the corresponding molecules in the original primitive cell [11]. Thus, the minimization procedure involves six degrees of freedom for the (2 · 2) structure (S 1 ), and 12 degrees of freedom for the (2 · 4) structure (S 2 ).…”

“…The corresponding potential parameters [11,14] are given in Table 1. The neopentane molecules and the substrate are considered as rigid and indeformable bodies.…”

“…A wide range of techniques [6][7][8][9] are used to improve the knowledge of the adsorption process by giving information on the isosteric heat of adsorption and to assess phase diagrams. In parallel way, calculations based either on ab initio methods [10] or on semi-empirical interaction potentials [11] have been performed to interpret the experimental findings on the statics and dynamics of these molecular monolayers. The present work deals with both neutron diffraction experiments and theoretical interaction potential calculations of the neopentane monolayer adsorbed on the square symmetry surface MgO(0 0 1).…”