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The process of obtaining an absorption spectra involves passing a complete spectrum of light from the material under consideration. The material absorbs the specific wavelength and allows the rest to pass through. But the reason of this absorption is given as the specific quantum gaps between the various electronic energy levels in the material and when an electron jumps to a higher level only a specific wavelength photon is absorbed. But the higher energy state is considered to be unstable and thus the electron will fall back immediately and would again give the wavelength preventing any spectra to be formed. The same doubt is in emission spectra when used to describe various flame colours but the same doubts apply there too.

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The point is in the direction which the atom will radiate. It's most probably not going to be the same as the initial photon. –  Ali Jul 9 '13 at 18:38
    
Are you asking if something like stimulated emission could spoil the result? I guess under normal conditions without the excited level being pumped as in a laser, most of the material would be in its ground state such that not much stimulated emission occurs. –  Dilaton Jul 10 '13 at 11:06
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up vote 5 down vote accepted

You do not state your question clearly

But the higher energy state is considered to be unstable and thus the electron will fall back immediately and would again give the wavelength preventing any spectra to be formed. The same doubt is in emission spectra when used to describe various flame colours but the same doubts apply there too.

I suppose you are asking "why we can see absorption and emission spectra after all, if de-excitation happens almost immediately".

Consider what happens with light absorption : A beam of light falls on the sample and one of its photons with the appropriate energy excites the electron to a higher state. The electron almost instantaneously falls back into the ground state BUT it has now got the four pi spherical angles to be emitted in, instead of in the direction of the beam. If one puts the film/detector well away from the beam direction one will see the emission spectrum. The film in the direction of the beam will be depleted at the frequencies of the absorption and show up as dark lines.

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Thank you. That addresses my question so precisely that now I can claim a rare occurence-"a doubt solved perfectly" –  Satwik Pasani Jul 10 '13 at 7:35
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