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Electric fields may tune quantum-tunnelling reactions at temperatures near absolute zero by changing how quickly molecules tunnel—and, in one modeled case, which direction they tunnel. A 2021 computational study predicted these effects for three molecular systems. It did not demonstrate a working chemical switch in an experiment.
What the study found
In a peer-reviewed study published in Chemical Science, Omer Kirshenboim, Alexander Frenklah, and Sebastian Kozuch calculated how an oriented external electric field could affect quantum tunnelling in molecules at cryogenic temperatures. Their results show that both field strength and direction can matter: depending on the molecule and field configuration, the calculations predict changes in reaction rates, tunnelling behavior, and molecular stability.
The paper first appeared online on 15 December 2020 and was published in Chemical Science 12 (2021), pages 3179–3187. It is open access under a Creative Commons Attribution 3.0 Unported Licence. Read the paper.
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Quantum tunnelling lets a particle pass through an energy barrier that it could not cross by ordinary classical motion. In a molecule, that behavior can contribute to reactions even when the temperature is too low for conventional thermal activation to explain the process.
An electric field can interact with a molecule’s charge distribution and change the relative energies of configurations along a reaction pathway. Because an oriented field has a direction as well as a strength, rotating or reversing it can change the calculated energy landscape differently. The study therefore does not describe a simple universal “on” button: the effect depends on the specific molecule and the field’s orientation.
Three reactions, three different responses
| Modeled system | Reaction examined | What the calculations indicate |
|---|---|---|
| Pentalene | π-bond shifting | The field’s orientation affects the reaction. In one unexpected calculation, a field perpendicular to the molecular plane lowered the barrier but produced a much slower reaction rate. |
| Semibullvalene | Cope rearrangement | A field along one molecular axis breaks the symmetry between two wells in the potential-energy surface, favoring one rearrangement direction. Other orientations can leave the states degenerate and tune the tunnelling frequency. |
| Diazabicyclohexadiene | Cycloreversion to cyclobutadiene and nitrogen | The paper predicts field-dependent stabilization or rapid decomposition, depending on the configuration. |
These are computational examples, not reactions reported as controlled by an electric field in a laboratory. The authors’ abstract describes effects across the cases including rate changes, inversion of the Arrhenius relationship, deactivation of molecular fluxionality, and stabilization or rapid decomposition. Those outcomes are system-specific rather than interchangeable.
Semibullvalene: the closest thing to a directional switch
Semibullvalene can rearrange between two structures. In the model, an electric field along a particular molecular axis breaks the symmetry between the two wells, favoring the more stable rearrangement. Removing the field restores back-and-forth tunnelling in the calculation; reversing it changes which direction is favored. This is why the paper’s “switch” idea is best understood as a theoretical control concept, not a built device.
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For the cited maximum modeled Y-direction field, the authors calculated a semibullvalene tunnelling rate of 2.1 × 10⁻³ s⁻¹, compared with 8.2 × 10⁻⁶ s⁻¹ for the zero-field case. These are rates from that specific model, not measured laboratory rates or values that can be generalized to other cold reactions. The paper also reports an exothermicity of up to −6.3 kJ mol⁻¹ for the cited strongest-field case.
Why this is not yet a practical chemical switch
The authors present the work as a proof of concept and note the difficulty of building an experimental setup to test it. The calculations motivate experiments; they do not establish that a device can already direct reactions this way in practice.
The environment also matters. The paper discusses the distinction between isolated gas-phase molecules and molecules held in cryogenic matrices. In a matrix, surrounding frozen material can affect reactivity, so results for an isolated molecule do not automatically describe a molecule embedded in a solid environment. The study’s predictions should be read within those modeling limits.
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What the result means
The study suggests a route for investigating whether electric fields can steer tunnelling-driven chemistry under ultracold conditions. Its clearest message is not that one field controls every reaction, but that carefully oriented fields may reshape particular molecular pathways. Whether this translates into experimental control remains an open question.
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