UV Absorption Spectra of Molecules

A useful starting point in the assessment of the nature of intrinsic valence-electron states in molecular solids is the comparison of the gas-phase and solid-state photoemission and UV absorption spectra of molecules whose radical cation geometries are expected to be the same in the two phases, e.g., S, Se., benzene, p-tetracyanoquinodimethane (TCNQ), and the polyacenes. One finds that in these cases the valence-electron photoemission spectra are shifted rigidly to lower binding energies by an intermolecular relaxation enemies 1 eV E (inter) 2 eV and are broadened considerably. This resuA indicates that the... 

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