Disentangling Auger decays in O2 by photoelectron-ion coincidences

Abstract

Abstract In non-resonant Auger electron spectroscopies, multi core-ionized states lead to numerous energetically close-lying electronic transitions in Auger spectra, this hampering the assignment and interpretation of the experimental results. Here we reveal a new method to overcome this intrinsic limitation of non-resonant inner-shell spectroscopies. In a proof-of-principle experiment performed for the O2 molecule, most of the Auger final states are dissociative, and we measure in coincidence the kinetic energy of the photoelectron and the kinetic energy release of the (O+, O+) ion pairs produced after the Auger decay of the O 1s−1 core-ionized states. The Auger final states are assigned using energy conservation. We fully separate the contributions from the 4Σ− and 2Σ− intermediate ionic states and conclusively demonstrate that the Auger decay probability can dramatically depend on the different O2 1s −1 intermediate multiplet states. In addition, a metastable Auger final state also exists, with lifetime longer than 3.8 μs, and clear changes are observed in both branching ratio and spectral profile of the O 1s photoelectron spectrum when they are recorded in coincidence with either $${{\bf{O}}}_{{\bf{2}}}^{{\boldsymbol{+}}{\boldsymbol{+}}}$$ O 2 + + or with other ionic species. These changes are attributed to the population of the metastable $${{\boldsymbol{B}}}^{{\boldsymbol{^{\prime} }}3}{{\boldsymbol{\Sigma }}}_{{\boldsymbol{u}}}^{-}({\boldsymbol{\nu }}{\boldsymbol{^{\prime\prime} }}{\boldsymbol{=}}0)$$ B ′ 3 Σ u − ( ν ″ = 0 ) Auger final state via different intermediate states.