Vibronic coupling and ion recoil effects in valence photoemission from chemisorbed molecules

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Abstract
To understand valence photoemission line shapes from chemisorbed molecules we must deal with hole delocalization through valence interactions, hole-vibration coupling, finite-temperature effects, and the finite lifetime of the final-state hole and of the vibration quanta. Moreover, ion recoil during the photoemission event should produce important line-shape changes if the experiment involves light atoms and high-energy radiation. An idealized, exactly soluble model provides a unified treatment of all these effects and the results differ qualitatively from those of previous partial and approximate treatments. In particular, it is found that a strong interaction of the molecular orbital with the valence continuum does not necessarily preclude observing the vibrational structure and its enhancement due to ion-core recoil.