  The basic theory of photoemission, inverse photoemission, Auger-electron and
appearance-potential spectroscopy is developed within a unified framework
starting from Fermi's golden rule. The spin-resolved and temperature-dependent
appearance-potential spectroscopy of band-ferromagnetic transition metals is
studied in detail. It is shown that the consideration of electron correlations
and orbitally resolved transition-matrix elements is essential for a
quantitative agreement with experiments for Ni.
