Doppler, collision, and

In order to compare the different contributions to the width of a spectral line, let us take as an example an atom of atomic mass A=100 having an excited level with a lifetime of lO s, which radiates at 5000 %. The gas temperature 

Natural width Collisional width Doppler width Units 

Although we have considered the various contributions to the width of spectral lines separately, it is obvious that in any experimental situation several effects will usually be acting simultaneously. Consequently the observed lineshape will not have either a simple Lorentzian or Gaussian profile. To investigate this we consider a moving atom whose resonance frequency is observed to be at Uq. 

Due to collisions or to the finite radiative lifetime the emitted radiation cons-lsts of a distribution of frequencies 0) about the centre frequency which is given by the Lorentzian function 

The resulting line profile has the form of a folding integral of the Lorentzian and Gaussian distributions  

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