DYNAMIC AND STATIC INTERACTIONS IN CO LAYERS ADSORBED ON MGO SMOKE (100) FACELETS - A FTIR AND HRTEM STUDY

MgO smoke showing highly perfect microcrystals was prepared by combustion of magnesium in air. High-resolution electron microscopy (HRTEM) indicated that the faces of MgO cubelets exhibit surface perfection to the extent that there is only a 5% departure from an ideal atomic (100) face. This constitutes a favourable condition to study static and dynamic interactions in an adsorbed layer. Spectra of CO adsorbed at 77 K on Mg2+ cations exposed on the (100) surface planes were obtained by Fourier-transform infrared (FTIR) measurements. A sharp peak at 2148.1 cm-1 (FWHM = 4.5 cm-1) is observed at maximum CO coverages. The CO stretching frequency of isolated molecules (CO "singletone") is 2156.0 cm-1. Dynamic and static effects, measured by using (CO)-C-12-(CO)-C-13 mixtures (dilution limit), are: DELTA-nu(dyn) approximately = 3.4 cm-1; DELTA-nu(stat) approximately = -11.3 cm-1. Dynamic polarizability (alpha(v)) of adsorbed CO was derived to be 0.0306 angstrom 3. These results are compared with those of CO on halide single crystals, showing that flat regions on (100) faces on MgO smoke microcrystals are large enough to simulate the behaviour of single crystal planes.