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Photons nay be emitted from hydrogen at, say 656.28 nm but, I guess in accordance with time-frequency uncertainty, the emission spectrum has a small finite width. This finite width can be wider for emission spectra with shorter decay times, if my understanding is correct.

Spectral emissions are usually given as very precise frequencies. Are these approximations?

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  • $\begingroup$ See this answer physics.stackexchange.com/questions/443054/… $\endgroup$
    – user213887
    Commented Dec 7, 2018 at 15:34
  • $\begingroup$ @JulianIngham-- Thank you, it's a very nice answer to this question. $\endgroup$
    – daniel
    Commented Dec 7, 2018 at 15:36

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There exists a "small finite width" for each of the lines of the spectrum due to the uncertainty principle.

What you are describing is called "natural broadening". Other effects which contribute to increase lines width are "Doppler broadening" and "pressure broadening", among others (I'm not taking into account uncertainties due to experimental devices).

As a result you do not obtain a Dirac's delta for each spectral line, but a distribution with some width. You can estimate from it the average frequency.

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  • $\begingroup$ I said the opposite: shorter decay times imply a bigger spread in frequency due to the uncertainty relation. If I'm not mistaken, the spread in frequency can be used to infer the decay time... $\endgroup$
    – daniel
    Commented Apr 30, 2017 at 19:39
  • $\begingroup$ Yes, I didn't read that well :) How can you know the decay time if you know the spread in frequency? $\endgroup$
    – falgenint
    Commented Apr 30, 2017 at 19:45
  • $\begingroup$ Uncertainty gives that $\Delta f\Delta t \geq k.$ If you have a handle on $\Delta f...$ $\endgroup$
    – daniel
    Commented Apr 30, 2017 at 19:49
  • $\begingroup$ I was thinking on other thing... my english is not very well, I'm sorry... but that's it, you are right! $\endgroup$
    – falgenint
    Commented Apr 30, 2017 at 20:05
  • $\begingroup$ Is the reported frequency an average? Can you cite a reference? $\endgroup$
    – daniel
    Commented May 1, 2017 at 18:31

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