Symmetry, selection rules and nomenclature in surface spectroscopies

The widespread use of techniques such as vibrational spectroscopy and photoelectron spectroscopy for the investigation of adsorbates on single crystal surfaces has focussed attention on the symmetry properties of adsorbed molecules and on the application of selection rules. In much published work, however, confusion exists as to the appropriate point groups and, in the case of ordered overlayers, the appropriate space groups. In this document, the symmetry properties of clean and adsorbate-covered single crystals are described, appropriate nomenclature suggested and the physical principles leading to selection rules in surface spectroscopies briefly listed.