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Isotope-induced partial localization of core electrons in the homonuclear molecule N2

Abstract

Because of inversion symmetry and particle exchange, all constituents of homonuclear diatomic molecules are in a quantum mechanically non-local coherent state; this includes the nuclei and deep-lying core electrons. Hence, the molecular photoemission can be regarded as a natural double-slit experiment1: coherent electron emission originates from two identical sites, and should give rise to characteristic interference patterns2. However, the quantum coherence is obscured if the two possible symmetry states of the electronic wavefunction (‘gerade’ and ‘ungerade’) are degenerate; the sum of the two exactly resembles the distinguishable, incoherent emission from two localized core sites. Here we observe the coherence of core electrons in N2 through a direct measurement of the interference exhibited in their emission. We also explore the gradual transition to a symmetry-broken system of localized electrons by comparing different isotope-substituted species—a phenomenon analogous to the acquisition of partial ‘which-way’ information in macroscopic double-slit experiments3.

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Figure 1: Experimental set-up for a photoelectron-fragment ion coincidence experiment at a synchrotron radiation source.
Figure 2: Symmetry resolved photoelectron distributions in the molecule frame.
Figure 3: Photoelectron angular distribution parameter β for N 2 :N(1 s ) electron emission in the photon-energy range 410–450 eV.
Figure 4: Isotope effect on N2.

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Acknowledgements

We thank J. Bozek, R. Diéz Muiño, F. J. García de Abajo, C. S. Fadley and M. A. Van Hove for many discussions about core–hole delocalization and coherent photoelectron emission in homonuclear molecules. The assistance of R. Püttner and F. Gelmukhanov in the interpretation of the effect of isotope substitution on the vibrational structure and the Franck–Condon factors is also acknowledged. The work was partly supported by the Bundesministerium für Bildung und Forschung (BMBF) and the Alexander von Humboldt Foundation (B.Z.).

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Correspondence to Uwe Becker.

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Rolles, D., Braune, M., Cvejanović, S. et al. Isotope-induced partial localization of core electrons in the homonuclear molecule N2. Nature 437, 711–715 (2005). https://doi.org/10.1038/nature04040

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