Atoms and molecules have temperature-caused random movements, so emission frequencies shift by Doppler effect {Doppler broadening}. Higher temperature makes more Doppler broadening. Higher mass makes less Doppler broadening. Higher frequency makes more Doppler broadening. Microwaves have lower frequencies than optical waves and so have lower Doppler broadening.
Hydrogen-atom electrons can be in 1s orbital or 1p orbital. Hydrogen-atom 1s-to-1p electronic transition has the smallest electronic-transition energy, equivalent to microwave photons. Microwaves have lower frequencies than optical waves and so have smaller Doppler broadening. This system is optimum to measure the fine-structure constant. Microwaves excite hydrogen-atom same-spin electrons from 1s to 1p orbitals {Lamb shift, electron} [1947] (Willis E. Lamb, Jr., and Robert Retherford) (Hans Bethe) to measure the fine-structure constant, which indicates virtual photons.
5-Physics-Matter-Atom-Wavelength Change
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Date Modified: 2022.0225