Theoreticly, the width of the spectral line in AAS (atomic absorbtion spectroscopy) is 10^-5, but in fact there happens an extention of it and it becomes 0.002-0.005. There are some factors which lead to this extention. Most common types of extentions are :

  1. Doppler extention
  2. Pressure extention
  3. Self-absorbance extention.

Does anyone know how to explain in a simple way why do these 3 kinds of extentions take place?

Do these deviations happen all the time in these measurments or are they some deviations that can happen in case the concentration of atoms is to high?

  • 2
    $\begingroup$ I think you mean "extension", or more commonly called "broadening". Have you tried maybe to consult some textbook or wikipedia? en.wikipedia.org/wiki/Spectral_line $\endgroup$
    – Greg
    Apr 29, 2015 at 11:08

1 Answer 1


From this source broadenings occur due to

  1. Doppler effect This effect arises because atoms will have different components of velocity along the line of observation. enter image description here
  2. Lorentz effect This effect occurs as a result of the concentration of foreign atoms present in the environment of the emitting or absorbing atoms. The magnitude of the broadening varies with the pressure of the foreign gases and their physical properties.

  3. Quenching effect In a low-pressure spectral source, quenching collision can occur in flames as the result of the presence of foreign gas molecules with vibration levels very close to the excited state of the resonance line.

  4. Self absorption or self-reversal effect The atoms of the same kind as that emitting radiation will absorb maximum radiation at the center of the line than at the wings, resulting in the change of shape of the line as well as its intensity. This effect becomes serious if the vapor, which is absorbing radiation is considerably cooler than that which is emitting radiation.

As Greg pointed out in the comment, You can find more detailed explanation on the topic here

Pressure broadening should be dependent on the concentration of atoms. The other type of broadening shouldn't be dependent on the concentration

  • $\begingroup$ Thanks a lot, do you have any idea about the last question I made ? Because all these things you mentioned are very likely to happen all the time ? $\endgroup$ Apr 29, 2015 at 18:00

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