Photoionization of molecular Rydberg states: H2, C 1Πu and its doubly excited states

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Abstract
Explanations are offered for some anomalies seen in photoelectron spectra resulting from single‐photon ionization of unperturbed single‐configuration Rydberg states of molecules. Some anomalous behavior may be due to occurrence of Cooper minima and shape resonances. Stronger effects can be due to excitation of the ion core producing doubly excited states whose decay characteristics and their effects on photoelectron spectra are discussed. As an example, anomalous photoelectron spectra produced in resonant multiphoton ionization of H2 via its C state are attributed to the excitation and autoionization of the 1Πg(2pσ)(2pπ) state. Formation of excited atomic hydrogen is predicted. The value of such experiments in investigating doubly excited states in general is discussed as well as the problem of preparation of ions in selected states.