Chemistry: Are there "spirits ties"?

Sophisticated manipulation brings atoms to chemical bond with empty space

This is what the spirit bond looks like: A hydrogen atom (red) in the Rydberg state binds with an empty spot in the RAUM. © M. Eiles / Purdue University
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Binding without a partner: Researchers have presented an impossible phenomenon: the chemical bonding of an atom to nothing. The electron of an excited hydrogen atom reacts to an empty space in the space - and behaves as if there were a reaction partner there. Such a "spirit bond" would be extremely short-lived, but still detectable, say the physicists. Still, however, the proof is in an experiment.

In chemistry, the rules are actually clear: A chemical bond always comes about when the outer electrons of one atom interact with those of another. Thus, it seems clear that there must always be at least two binding partners, and in rare cases true three-partner reactions may occur, as researchers have recently discovered. Whether a bond is present can be read off, inter alia, from the shape of the electron orbitals.

At the beginning there is a giant atom

But what if you could trick an atom into reacting with a nonexistent partner? What sounds absurd is Matthew Eiles of Purdue University and his colleagues. They developed a method to create such a bond with nothingness - a "ghost bond". In a theoretical simulation, they prove that and how this is possible.

At the heart of this "ghost bond" is a Rydberg atom - an atom in which the outer electron circles extremely far out through the supply of energy. The atomic shell is thus bloated up to a thousandfold. "Experiments in recent years have shown that completely new forms of bonding can occur between such excited Rydberg atoms and a ground-state atom, " reports Eiles. "The resulting electron orbitals are similar to a prehistoric trilobite fossil."

Orbital as a real bond

Eiles and his team have now used this exotic bond as a starting point for their "spirit bond". To generate these, one first has to convert a hydrogen atom into a Rydberg atom by laser irradiation. Then a well-balanced sequence of magnetic and electrical pulses makes the electron think of itself as a binding partner: the pulse combination mimics the potential that occurs when the Rydberg atom binds to a partner. display

This manipulation causes the electron to remain localized at one point in the space instead of roaming freely, the researchers report. The electron appears to be bound to an invisible partner although there is nothing there but empty space. Nevertheless, as with a true bond, the electron's probability of residence changes and the orbitals take on a trilobite form.

Short lived, but detectable

"The production of these exotic chemical bonds is based on the fact that Rydberg electrons are particularly easily influenced by external fields, " explain Eiles and his colleagues. Due to their large distance from the atomic nucleus, they are less controlled by them and therefore react even to comparatively weak influences from outside. That makes it easier to manipulate their wave function, the researchers said.

However, this "ghost tie" does not last long: "We assume a lower life of around 200 microseconds, " say the scientists. However, by cooling down the Rydberg atom to ten Kelvin, it could take several milliseconds to complete. Evidence could then be provided to explain exotic ghost binding by means of X-ray diffraction or electron spectroscopy, as Eiles and his colleagues say.

How feasible are the spirit ties?

So far, however, such atomic bonds exist with nothingness only on paper. The problem: To create the ghost bond, the magnetic and electrical pulses must be balanced extremely precisely. Their amplitude, the timing of the pulses and the field strength must have very specific values ​​ and this is very difficult to achieve with previous technology, as the researchers explain. In addition, the entire experiment has to be completely shielded from background fields.

However, Eiles and his team believe that creating ghost bonds in the near future is feasible. "You could even imagine more exotic 'ghost' states, where triplets are simulated or multiple 'ghost' atoms line up, " the researchers speculate. (Physical Review Letters, 2018; doi: 10.1103 / PhysRevLett.121.113203)

(American Institute of Physics, 19.09.2018 - NPO)