PE spectra were recorded on a Leybold-Heraeus UPG 200 spectrometer
with He(I) excitation (21.21 eV, 58.46 nm) and were calibrated with lines
of xenon (12.13 and 13.44 eV) and argon (15.76 and 15.94 eV). The resolution
of the spectrometer is 0.02 eV, in the range of broad and overlapping bands
about 0.05 eV.