Ghost Chemical Bond | A Whole New Perspective Of Bonding Atoms

  • A sequence of electric and magnetic pulses could force electrons to behave as if bonded to a nonexistent atom. 
  • This temporary bond should exist for more than 200 microseconds.

A chemical bond is the most basic fundamental of chemistry that explains why atoms are attracted to one another and how chemical reactions form a product. This force of attraction can be seen as a result of different behaviors of valence electrons (in outermost shell) of atoms.

All elements are distinguishable from each other: they have unique electron-cloud, a region where electrons move around the atom’s nucleus. This electron cloud determines chemical properties of the atom and its willingness to accept/give up valance electron from/to another atom.

To form a chemical bond, it requires a minimum of two atoms. However, a new study may cut down that requirement to just one. Recently, researchers at Purdue University discovered a new method to create a trilobite bond by tweaking a Rydberg atom (an excited atom with one or more electrons comprised of a high principal quantum number).

Creating A Ghost Bond

In the last couple of years, researchers have detected trilobite bonds in unique diatomic molecules like Carbon disulfide (Cs2) and Rubidium (Rb2). In such scenarios, one of the atoms remains in a ground state, while the other remains in a Rydberg state.

Since the outer electron of Rydberg atom occupies a distant orbit, trilobite molecules are enormously big in size, nearly a thousand times bigger than conventional diatomic molecules.

Researchers used numerical analysis to demonstrate that a particular series of alternating electric and magnetic field pulses can change the Rydberg hydrogen atom’s electronic wave function to match the characteristics of a trilobite molecule.

Reference:  arXiv:1806.02963 | APS Physics 

Strangely, this localizes the excited electron to a fixed point in empty space that is several nanometers far from the nucleus. According to the numerical analysis, this temporary bond between the Rydberg atom and a virtual ‘ghost’ atom should exist for more than 200 microseconds.

ghost chemical bondArtistic concept of ghost chemical bond | Credit: Matthew Eiles / Purdue University

Technical details: 

In this study, the time evolution is determined by unitary operators in degenerate first-order perturbation theory. The field sequence to ensure perfect overlap with a target state is optimized via a gradient ascent algorithm obtained from optimal control theory. Furthermore, two detection approaches are presented to investigate the chemical bond, either in the true trilobite or ghost molecule.

What’s Next?

In the future, experimental physicists will try to synchronize the pulses and block external fields to meet these strict requirements. If they succeed in overcoming all hurdles, and create a ghost bond, it could be observed through X-ray- or electron scattering tests.

Read: The First Simulation Of Chemical Bonds On A Quantum Computer

Of course, applications of this theoretical bond are speculative, but researchers believe that it has the potential to modify rates of chemical reaction to some extent. Moreover, the theory could be extended to atoms with quantum defects or implemented precisely to incorporate nonperturbative field effects.

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