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Electric fields may tune the speed and direction of certain quantum-tunnelling reactions at temperatures near absolute zero—but the “switch” is a theoretical idea, not a device or reaction control demonstrated in a laboratory. A 2021 computational study found that the effects depend on both the field’s strength and its orientation relative to the molecule.
What the study found
In a peer-reviewed paper published in Chemical Science, Omer Kirshenboim, Alexander Frenklah and Sebastian Kozuch modeled how oriented electric fields affect tunnelling in three molecular reactions. The paper first appeared online on 15 December 2020 and was published in volume 12 (2021), pages 3179–3187. It is open access under a Creative Commons Attribution 3.0 Unported Licence. Read the paper, “Switch chemistry at cryogenic conditions: quantum tunnelling under electric fields”.
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Quantum tunnelling allows a particle to pass through an energy barrier that classical physics would require it to climb over. At very low temperatures, tunnelling can contribute to chemical reactions when ordinary thermal energy is limited. The calculations examined whether an external electric field could alter that process by changing the molecules’ energy landscape.
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The authors’ central result is conditional rather than universal: changing either field strength or direction can change reaction kinetics, but the response differs among molecules. The paper’s abstract describes the effects as “subtle but remarkable changes.”
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How the three molecular examples responded
The calculations covered three distinct reactions, so their outcomes should not be treated as interchangeable.
| Modeled system | Reaction | What the field calculations showed |
|---|---|---|
| Pentalene | π-bond shifting | The field’s orientation could produce an unexpected rate response. The authors reported that a field perpendicular to the molecular plane lowered the barrier yet made the calculated reaction much slower. |
| Semibullvalene | Cope rearrangement | Depending on direction, the field could break the symmetry between two potential-energy wells, favor one rearrangement direction, or leave the states degenerate while tuning tunnelling frequency. |
| Diazabicyclohexadiene | Cycloreversion to cyclobutadiene and nitrogen | The paper’s abstract reports field-dependent stabilization or rapid decomposition in this case; the outcome depends on the field configuration. |
For the pentalene result, study author Sebastian Kozuch told Chemistry World that the team expected a field to make the reaction somewhat faster or slower depending on direction, but found that the perpendicular orientation lowered the barrier while slowing the calculated rate.
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Why field direction matters in semibullvalene
Semibullvalene can tunnel between two configurations represented by wells in a potential-energy surface. In the model, applying a field along one molecular axis makes those wells unequal in energy. That asymmetry favors the more stable rearrangement instead of the balanced back-and-forth tunnelling predicted without the field. Removing the field restores that back-and-forth behavior in the calculation; reversing the field changes which direction is favored.
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A free scan shows the junk files, broken settings and background clutter dragging Windows down - then fixes them in one click.Free scan · Windows 10 & 11Other field orientations do not necessarily split the two states. When the states remain degenerate, the field can instead alter the tunnelling frequency. Thus, “switching” describes a proposed way to bias or tune a modeled reaction, not a single on/off mechanism that works the same way for every molecule.
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What the calculated rates mean
For semibullvalene, the authors calculated a tunnelling rate of 2.1 × 10−3 s−1 at the maximum modeled Y-direction field they considered, compared with 8.2 × 10−6 s−1 in the no-field calculation. These are rates from that model and configuration, not laboratory measurements or general values for cold reactions. The paper also reports an exothermicity of up to −6.3 kJ mol−1 for the cited strongest-field case.
Across the three examples, the authors’ abstract describes a range of predicted effects: changes in rate, inversion of the Arrhenius relationship, deactivation of molecular fluxionality, and stabilization or rapid decomposition in the cycloreversion system. These are different outcomes in different modeled systems, not a claim that every reaction exhibits all of them.
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What has—and has not—been demonstrated
The work is a computational proof of concept. It does not report a working experimental switch or field-controlled reactions performed in a lab. The authors note that constructing an experimental setup would be difficult, and frame the calculations as a starting point for further work.
The environment also matters. An isolated gas-phase molecule and a molecule held in a cryogenic matrix are not equivalent: the frozen surroundings can themselves affect reactivity. The calculated behavior therefore should not be read as a ready-made prediction for every molecule or experimental setting.
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The finding is significant as a control concept: it suggests that an oriented electric field could provide another way to influence tunnelling chemistry under ultra-low-temperature conditions. Whether that control can be implemented experimentally remains an open challenge.
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