Localization and loss of coherence in molecular double-slit experiments

Abstract

In molecular double-slit experiments, the interference between emitted core electrons of diatomic molecules gives rise to oscillations in the observed electron intensity. Here, we explore this behaviour for photoelectrons emitted from CO and N2 by soft X-ray ionization in the molecular frame, and we argue that in addition to the undisturbed emission process, intramolecular scattering can lead to electron interference between the scattered and unscattered wave in two ways: two-centre interference between two spatially coherent emitters and one-centre self-interference. The latter is the signature of a loss of spatial coherence. The spatial scale over which the transition from two-centre to one-centre coherence occurs is the de Broglie wavelength of the scattered photoelectron in units of the bond length. These results highlight the fact that the molecular double slit is based on two independent uncertainty principles, ΔpxΔx and ΔEΔt, the second of which causes ongoing tunnelling between the two centres, even after the collapse of the electron wavefunction in real space.

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Figure 1: Schematic diagram of the gas-phase photoelectron diffraction experiment on CO.
Figure 2: Photoelectron diffraction intensities versus electron momentum k and de Broglie wavelength λ (in units of the internuclear distance R) for CO molecules in the gas phase.
Figure 3: Schematic diagram of the experimental set-up for the high-resolution angle-resolved photoelectron–fragment ion coincidence experiment on N2.
Figure 4: Photoelectron diffraction intensity versus electron kinetic energy for electron emission along the direction of the molecular axis in the homonuclear molecule N2.
Figure 5: Scattering behaviour of the N+2(N(1s):g, u) photoelectrons.

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Acknowledgements

The authors acknowledge financial support by the Bundesministerium für Bildung und Forschung (BMBF Contract No. 05KS4EB1/3). B.Z. and D.R. thank the Alexander von Humboldt Foundation for a Feodor Lynen fellowship. The authors are grateful to David Shirley for providing the initial beam time for this project at the Advanced Light Source. They also thank E. Moler for his help during this initial period, G. Prümper for his contribution to the development and implementation of the detector and D. Dowek and A. Roy for helpful comments and critical reading of the manuscript.

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The calculations were carried out by B.Z. and V.M., whereas the measurements and the analysis of the experimental data were done by the other authors.

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Correspondence to Uwe Becker.

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Zimmermann, B., Rolles, D., Langer, B. et al. Localization and loss of coherence in molecular double-slit experiments. Nature Phys 4, 649–655 (2008). https://doi.org/10.1038/nphys993

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