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Classical diffusion—quantum barrier: On Cu(111), pyrrole diffuses in channels, hopping between adjacent bridge sites over a barrier above hollow sites. The motion of the center of mass can be described classically; however, the activation barrier arises from the quantum character of internal vibrational modes that are largely unexcited during the motion. The unique helium spin‐echo experiment is indicated by the green sphere and arrows. [ABSTRACT FROM AUTHOR]

Molecules are commonly thought of as classical objects obeying Newtonian mechanics. However, in their Communication on page 5085 ff., B. A. J. Lechner et al. describe how the diffusion of pyrrole on a Cu(111) surface is determined by the quantum character of the internal vibrations of the molecule. Bending and torsion modes are found to be responsible for the tripling of the barrier to diffusion through lateral changes in their zero point energies. [ABSTRACT FROM AUTHOR]

Bei Molekülen denkt man gemeinhin an klassische Objekte, die den Newtonschen Gesetzen folgen. B. A. J. Lechner et al. beschreiben in ihrer Zuschrift auf S. 5189 ff. aber, wie die Diffusion von Pyrrol auf einer Cu(111) ‐ Oberfläche durch den Quantencharakter der inneren Schwingungen des Moleküls bestimmt wird. Biege ‐ und Torsionsmoden erweisen sich als verantwortlich für die Verdreifachung der Diffusionsbarriere durch laterale Änderungen ihrer Nullpunktsenergien. [ABSTRACT FROM AUTHOR]