Electronic structure of adsorbed organic molecules

We report on investigations of chiral organic molecules in the gas phase and physisorbed on graphite. The measurements were carried out by means of angle-resolving VUV photoelectron spectroscopy. The emission from specific orbitals in oriented molecules can be forbidden because of dipole selection rules. Due to the lack of certain features in the spectra, it was possible to determine the adsorption geometry of cyclohexanone and camphor as being with their ring system parallel to the surface. By comparison of gasphase and adsorbate spectra of ethyl benzene derivatives, adsorption could be proved to be molecular without decomposition. For amino acids on graphite, the occurrence of characteristic features gives direct evidence for molecular adsorption, despite of their very low vapor pressure in the gas phase.