THE C1S CORE BINDING-ENERGY SHIFTS OF ETHENE, 1,3-BUTADIENE, 1,3,5-HEXATRIENE - THE ANALOG TO A SURFACE SHIFT OBSERVED ON A QUASI ONE-DIMENSIONAL SYSTEM

The core hole photoelectron spectra of ethene, 1,3-butadiene and 1,3,5-hexatriene are studied as model molecules, i.e. monomer, dimer and trimer subunits of polyacetylene. The C 1s photoelectron spectra show partially resolved lines for both 1,3-butadiene and the 1,3,5-hexatriene. The chemical shifts between the terminal and nonterminal carbons have been experimentally determined via assignments of the gas phase spectra supported by core-hole-relaxed DELTASCF ab initio calculations. By plotting the measured core-hole binding energies against a connectivity number the binding energies relative to the vacuum level of different carbon atoms in the semi-infinite one-dimensional quasi-crystal can be extrapolated. The experimental C 1s chemical shifts determined in this way show an oscillatory behaviour for the carbon atoms near the boundary of the quasi-infinite chain.