Near-threshold photoionisation theory for diatomic molecules

Abstract

An integral variant of multichannel quantum defect theory is suggested for studying the near-threshold photoionisation of non-symmetrical molecules of the type XY. The main problem here is to express the dipole transition matrix element through corresponding adiabatic parameters of the e-+XY+ system and to reveal its dependence on the incident photon energy. The resonance structure of absorption spectra near the ionisation threshold is shown to be completely determined by the energy dependence of the partial amplitudes of electron-ion scattering that may be investigated independently. Various limits and special cases which demonstrate peculiarities of the interference structure of absorption spectra as well as the role of different factors in the formation of the line profile are considered.