Recent Developments in the Calculation of Molecular Auger Spectra

Abstract

The spectroscopy and dynamics of doubly charged molecular cations in the gas phase are nowadays intensively studied by means of several complementary experimental techniques. In the oldest exploited class of experiments dications are produced by decay of core ionized molecules via electron emission. This is the basis of Auger electron spectroscopy (AES) [1], where the number of emitted electrons is measured as a function of their kinetic energy. In recent developments, vibrationally resolved Auger spectra have been obtained [2–4] and additional information on the nature of the dicationic states populated can be gained via the coincidence detection of Auger electrons and the sufficiently long-lived dications or their fragmentation products [5,6]. In a second important class of techniques the doubly charged cations are produced directly from their neutral parent species. In double charge transfer spectroscopy [7] this is achieved by collision of protons impinging on the target molecules. The one-step two-electron removal channel can be identified by its specific pressure dependence and the energy loss of the detected H- ions is measured. Dicationic species can also be obtained by electron impact, and their lowest lying states observed by translational energy loss spectroscopy [8], or by collisional charge stripping from singly charged precursors [9]. Finally, in recent years, new powerful techniques have been successfully established, [10–12] based on direct double photoionization from synchrotron radiation, followed by the coincidence detection of photoelectrons and/or photoions (either long-lived dications or charged fragments).