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I know that many reactions produce visible light, heat and sound, but is there a reaction (preferably one example for an inorganic and organic one) that could produce electromagnetic waves in the microwave and radio band?

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  • $\begingroup$ Interestingly, the reaction *H + *OH -> H2O + Photon (of Light) but no radiation. $\endgroup$ – AJKOER May 1 at 19:54
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    $\begingroup$ Explosions produce high velocities and dust and that combination can produce moving charge and that can produce radio noise. Radio noise from dust storms is a known phenomenon on Mars, but this is probably too much of a stretch for this question. Also I think pulling tape can make RF noise for similar reasons, electric charge flow can even make X-rays! nytimes.com/2008/10/28/science/28xray.html $\endgroup$ – uhoh May 2 at 4:56
  • $\begingroup$ The production of microwave radiation probably accompanies most any exothermic reaction in which a molecule is the product, because microwave radiation results from rotational motion (and occasionally barrier tunnelling as in NH3) and exothermic reactions initially have a non-boltzmann distribution of energies. Only in magnetic fields as in an NMR machine would you expect to emit radio frequency radiation as the energy gap here is far smaller than any molecular process such as rotation or vibration. $\endgroup$ – porphyrin May 8 at 9:14
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An ammonia maser qualifies as an inorganic RF-emitting reaction. As the nitrogen changes position in the $\ce{NH3}$ molecule, ~24 GHz radiation is emitted.

Similarly, organic methanol, $\ce{CH3OH}$ makes a maser found in nature, emitting at ~36.2 GHz and also at ~6.7 GHz.

BTW, if the reactants are moving away rapidly (e.g. interstellar gases), visible radiation is red-shifted to microwaves... or lower, so wavelength depends on your frame of reference. So, as Brumley and Stevens state, listen in to radio astronomy.

Though these might be due to physical excitation, and not an exact answer for your question, an interesting experiment would be to form $\ce{NH3}$, e.g. with the Haber process, and try to detect the 24 GHz radiation, perhaps due to initial formation of the molecule in a metastable state, or due to rearrangement. A similar experiment could be done with methanol, forming it from $\ce{CO}$ and $\ce{H2}$, looking for 36.2 GHz or 6.7GHz signals. I'd be very interested to know if you or anyone else tries that!

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