Synopsis: How to Create a Ghost Chemical Bond

A series of electric and magnetic pulses applied to an atom could cause one of its electrons to behave as if “bonded” to an empty point in space.
Synopsis figure
M. Eiles/Purdue University

It goes without saying that a chemical bond requires, at the bare minimum, two consenting atoms. But a proposed experiment might reduce that requirement to just one, providing researchers with a new perspective on unusual chemical bonds. Matthew Eiles and colleagues at Purdue University in West Lafayette, Indiana, have come up with a way to construct a so-called trilobite bond—named after the electronic wave function’s resemblance to fossils of the long-extinct arthropod—by carefully manipulating a Rydberg atom, an atom with one electron in a highly excited state.

Normally, scientists have observed trilobite bonds in special types of diatomic molecules, such as Rb2 and Cs2. In these cases, one of the atoms is in a Rydberg state, while the other is in its ground state. Because the Rydberg’s pumped-up outer electron occupies a very distant orbital, these “trilobite molecules” are unusually large, about 1000 times larger than typical diatomic molecules. Using numerical analyses, Eiles and colleagues show that through a precise sequence of alternating electric and magnetic field pulses, the electronic wave function of a Rydberg hydrogen atom can be sculpted to match that of a trilobite molecule. This leaves the excited electron strongly localized to a point in space, dozens of nanometers from the nucleus. The wave function should persist for at least 200 𝜇s, in effect temporarily bonding the Rydberg atom to a nonexistent “ghost” atom.

Experimentalists will need to figure out how to accommodate the stringent requirements for synchronizing the pulses and blocking external fields. If these hurdles could be overcome and a ghost bond is produced, the system could be observed via electron- or x-ray-scattering experiments. While applications are speculative, the team imagines that it might be possible to see if such a preformed bond modifies chemical reaction rates in some way.

This research is published in Physical Review Letters.

–Christopher Crockett

Christopher Crockett is a freelance writer based in Arlington, Virginia.


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Atomic and Molecular Physics

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