STUDY OF THE VALENCE ELECTRONIC-STRUCTURE OF ETHYNE BY ELECTRON MOMENTUM SPECTROSCOPY AND GREEN-FUNCTION METHODS

The complete valence shell electron separation energy spectra and momentum distributions are measured for ethyne by high resolution electron momentum spectroscopy at a total energy of 1500 eV. Many-body calculations of the separation energies and spectroscopic factors using Green's function methods are carried out and compared with the data. The measured momentum distributions are compared with self-consistent-field (SCF) orbital wave functions, the SCF wave functions including d functions in the basis sets. The agreement between the measured momentum distributions and the SCF orbital momentum distributions is excellent. The inner valence 2-sigma-g orbital is found to be split severely by final state correlation effects. The agreement between the measured and calculated spectroscopic factors and separation energies is in general very good, although the measured separation energy spectra contain significant strength up to 50 eV, this strength being mainly of 2-sigma-g origin.