THE EFFECT OF CRYSTAL DEFECTS ON THE IONIZATION ENERGY OF ADSORBED DYE MOLECULES
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Publisher:Ohio State University
The experimental determination of the ionization energy of dye molecules adsorbed on substrates is complicated by an exponentially rising yield of photoelectrons per incident photon, with increasing photon energy. We have tested the hypothesis that the lattice defects of the substrate are causing a distribution of molecular ionization energies. Roothaan ‘s SCF formulation, for both closed and open shell configurations was used in the calculations, with the zero differential overlap approximation. The perturbation produced by defects was included by use of the uniformly charged sphere approximation, assigning an appropriate effective charge to the defect. It was found that for distances greater than the size of the molecule, the effect is given by the classical coulombic interaction. The situation where the defect is very close to the molecule is more complicated. Additivity was established for the effect of many defects. A Monte Carlo calculation gave the final distribution of molecular ionization energies. The distribution is an exponential one, for defect densities that are reasonable. The ionization energy of the unperturbed molecule corresponds to the peak of the distribution, giving a rational criterion for the experimental determination of the ionization energy.
Author Institution: Department of Physics, The Ohio State University
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