| Popis: |
High-resolution valence electron energy distributions are reported for monoclinic selenium ($m\ensuremath{-}\mathrm{S}\mathrm{e}$, i.e.,${\mathrm{Se}}_{8}$), trigonal selenium, and orthorhombic sulfur ($\ensuremath{\sigma}\ensuremath{-}\mathrm{S}$, i.e.,${\mathrm{S}}_{8}$). These data, as well as previously published optical spectra of ${\mathrm{Se}}_{8}$ are analyzed using our spectroscopically parametrized CNDO-S (complete neglect of differential overlap, spectroscopically parametrized) molecular-orbital model. The general features of the valence-electron spectra are regarded as direct consequences of the symmetry of the molecular units and the difference in $s$- and $p$-electron ionization potentials. Important details in the $s$-electron photoemission spectra and in the optical-absorption spectra, however, require the full power of the CNDO-S model for their interpretation. We conclude that the photoemission and optical-absorption spectra of $m\ensuremath{-}\mathrm{S}\mathrm{e}$, like those of $\ensuremath{\sigma}\ensuremath{-}\mathrm{S}$, can be interpreted directly in terms of the electronic structure of the individual ${\mathrm{Se}}_{8}$ and ${\mathrm{S}}_{8}$ molecules, respectively. |
