Studies of surfaces by electron spectroscopy

Abstract

All the organic molecules containing lone-pair orbitals adsorb molecularly (associatively) on copper at low temperatures (<100 K). b) It is possible to estimate the stabilization of the lone-pair orbitals due to chemisorption in terms of the increase in their binding energy. The shift in the lone-pair orbital due to chemisorption generally shows an increasing trend with the decreasing first ionization energy of the organic molecule, as expected (see Table III.3). c) Chemisorption of molecules gives rise to variation in the core-level binding energy of the atom containing the lone pair-O(1s) or N(1s) binding energy in the present study would be expected to vary just as in coordination compounds. After accounting for extramolecular relaxation/polarization shifts by matching C(1s) binding energies of adsorbates with those of free molecules, the O(1s) binding energies are found to increase by about 0.6 ± 0.2 eV in the case of methanol and acetone adsorbed on Cu. d) Warming the substrate to temperatures above 120 K generally results in the transformation of the adsorbate molecules in all cases, and the nature of the species produced depends on temperature, as can be seen from Table III.2. The transformation is not only reflected in changes in the valence region (in the UPS) but also in the C(1s) and O(1s) binding energies in XPS. It is interesting that methyl acetate gives the same transformation product on the copper surface as methanol (Table III.2). In the case of methyl amine, we find formation of a nitrogenous species. e) The results of our studies on the adsorption of organic molecules on copper find support from Auger studies carried out for the first time in this laboratory. Thus, Auger spectra also show the transformation of methanol to formaldehyde on the copper surface.

Stabilization of the Lone-Pair Orbitals (in eV) on Molecular Chemisorption on Copper

MoleculeLone-Pair I.E. (eV)Lone-Pair Shift (eV)Methanol10.90.5Methyl acetate10.50.3Acetone9.60.4Diethyl ether9.6-Methyl amine9.60.6 Note: This shift is of the carbonyl lone pair.