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.