Physics of molecular ion formation

The basic processes in molecular photoionization are reviewed in the light of classical and recent theoretical models and illustrated on O2 and N2O. Attention is given to the determination of ion energy levels by photoelectron spectroscopy, photoionization cross sections and ionization mechanisms, and recent experimental studies of partial photoionization cross sections. It is noted that photoionization cross section measurements show very rich spectra with both broad and fine irregular structures that cannot be understood in the light of the simplest theoretical models only, such as direct ionization and autoionization.