Structural Dynamics (Jul 2022)

Observation of intermolecular Coulombic decay and shake-up satellites in liquid ammonia

  • Hanns Christian Schewe,
  • Eva Muchová,
  • Michal Belina,
  • Tillmann Buttersack,
  • Dominik Stemer,
  • Robert Seidel,
  • Stephan Thürmer,
  • Petr Slavíček,
  • Bernd Winter

DOI
https://doi.org/10.1063/4.0000151
Journal volume & issue
Vol. 9, no. 4
pp. 044901 – 044901-12

Abstract

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We report the first nitrogen 1s Auger–Meitner electron spectrum from a liquid ammonia microjet at a temperature of ∼223 K (–50 °C) and compare it with the simultaneously measured spectrum for gas-phase ammonia. The spectra from both phases are interpreted with the assistance of high-level electronic structure and ab initio molecular dynamics calculations. In addition to the regular Auger–Meitner-electron features, we observe electron emission at kinetic energies of 374–388 eV, above the leading Auger–Meitner peak (3a12). Based on the electronic structure calculations, we assign this peak to a shake-up satellite in the gas phase, i.e., Auger–Meitner emission from an intermediate state with additional valence excitation present. The high-energy contribution is significantly enhanced in the liquid phase. We consider various mechanisms contributing to this feature. First, in analogy with other hydrogen-bonded liquids (noticeably water), the high-energy signal may be a signature for an ultrafast proton transfer taking place before the electronic decay (proton transfer mediated charge separation). The ab initio dynamical calculations show, however, that such a process is much slower than electronic decay and is, thus, very unlikely. Next, we consider a non-local version of the Auger–Meitner decay, the Intermolecular Coulombic Decay. The electronic structure calculations support an important contribution of this purely electronic mechanism. Finally, we discuss a non-local enhancement of the shake-up processes.