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# Rapid rotation explains unusual stability of C2 anion
- URL: https://balaustine.mymagic.page/rapid-rotation-explains-unusual-stability-of-c2-anion/
- Published: 2024-11-02T11:52:26.000Z
- Updated: 2026-08-23T11:27:10.000Z
- Author: VM
- Tags: Scicomm, centrifugal potential, decay modes, diatomic carbon, diatomic carbon anion, interstellar medium, #Migrated-1787484114599, #wp, #wp-post, #Import 2026-08-23 11:22

In various settings, including chemical reactions in the lab, inside nuclear reactors, and in outer space, scientists have found C2– anions living for as long as three milliseconds before decaying to a more stable state — and they haven’t been able to explain why. Normally particles, atoms, and molecules make these transitions to lose energy and become more stable. And normally the C2– molecule has around 4 eV less energy than the C2– anion, so the latter decayed to the former within one-trillionth of a second. The puzzle was that scientists didn’t know of a mechanism that allowed C2– to not decay to C2 for more than 3 ms, a timespan more than a billion-times longer.

In two new papers published on October 31 ([here](https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.133.183001?ref=balaustine.mymagic.page) and [here](https://journals.aps.org/pra/abstract/10.1103/PhysRevA.110.042828?ref=balaustine.mymagic.page)), researchers from Austria, the Czech Republic, and Germany reported “strong evidence” for an idea scientists first had in the late 1990s: that the delay had something to do with rotation. Scientists have previously found rapidly rotating molecules in space — including when radiation breaks up water molecules in the [interstellar medium](https://www.nature.com/articles/s41467-019-09176-z?ref=balaustine.mymagic.page) and in the [dynamic neighbourhood](https://iopscience.iop.org/article/10.1086/589998?ref=balaustine.mymagic.page) of a newborn star.

The study team found that when the C2– complex rotates fast enough to increase its rotation quantum number 𝑁 beyond 155, it acquires a “centrifugal potential” that rearranges the lower-energy states to which C2– can decay. In particular, the team’s theoretical calculations revealed that a different state other than the C2 state to which it normally decays has lower energy, and dropping to the C2 state becomes unfavourable. More specifically, if the C2– anion had 𝑁 values in the 165-183 range, the normal decay to C2 requires electrons to have at least six units of angular momentum. If 𝑁 is lower than 165, the rearrangement of energy states doesn’t forbid the rapid drop to C2.

In other words, the spinning molecule spits out a spinning electron to move to a more stable configuration — and even then not before living to the ripe old age of 3 ms. This so-called rotation-assisted stability of the C2– anion isn’t entirely new. Other scientists have previously found dihydrogen and dideuterium anions (H2– and D2–) to be more stable as well when 𝑁 = 20-40\. Using and theory and experiments, the European team found C2– acquired the same stability gain at 𝑁 of 155 or more because it’s heavier and has a higher rotational constant (“a fundamental parameter describing the rotational energy levels of a molecule,” per Meta AI).