![]() For π-conjugated organic molecules, these originate from linear combinations of only 2p z-orbitals on identical (all carbon) atoms. So far, the PWA has only been confirmed experimentally for π orbitals close to E F. īecause it is based on ARPES, POT per se is not limited to a particular binding energy range if the photon energy is large enough. This is valid if the final state of the photoelectron after photoemission can be represented by a plane wave (PW). There is overwhelming evidence that, for π orbitals in conjugated molecules, this relation is a straightforward Fourier transform ( 24, 25). The measured angular distribution of photoelectrons is governed by the spatial distribution of electrons in the initial state-the orbital. ![]() In contrast, in POT, photoelectrons are collected in the half-space above the sample surface on which the adsorbed molecules are fixed in space ( 7, 17– 19). While it has long been recognized that angle-resolved photoelectron spectroscopy (ARPES) can image orbitals in the molecular frame, the alignment of molecules in the gas phase is a challenge ( 21– 23). For example, valence spectra have been deconvolved model-free into orbital projected densities of states (pDOS) ( 15, 16), orbitals have been reconstructed from experimental data in two dimensions (2D) and 3D ( 17– 19), and orbital patterns in momentum space have been recorded with femtosecond time resolution ( 20). ![]() Photoemission orbital tomography (POT) ( 7) is a recent technique for the orbital analysis and orbital imaging of molecules on surfaces. ![]()
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