Molecular Excitons of Solid Carbon Dioxide

The fundamental absorption spectra of solid carbon dioxide are studied in the energy region from 9.2 eV to 30.0 eV, and the valence states are studied by means of X-ray photoelectron spectroscopy (XPS). The XPS spectra manifest that the electronic structure in solid phase is not very different from that in gas phase. The absorption spectra show four prominent peaks in the energy region from 10.0 eV to 12.0 eV, three of which are analyzed quantitatively as the excitons arising from the molecules in optically allowed excited states 1 Σ u + and \(¹ ᵤ\). The exciton excitation energies are calculated and show a good agreement with the experimental spectra. The \(¹ ᵤ\) state in gas phase is split into two by inter-molecular interactions in solid phase and gives rise to the peaks at 11.0 eV and 11.2 eV in the absorption spectra.