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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: nigel433 on October 24, 2010, 03:10:03 PM

Title: width of absorption lines
Post by: nigel433 on October 24, 2010, 03:10:03 PM

We are told that the absorption of EM radiation by an atom, resulting
in an electron jumping from one state to another, is very precise and
exact - in terms of the energy absorbed, and the frequency "deleted".

My question is HOW precise? If the phrase "exact energy match" is taken
literally then there will never be ANY noticeable energy taken out (for the
same reasoning as in mathematics, which implies that a precisely define
line has no width at all and therefore contributes ZERO area in an integration).

In other words "lines" in the absorption spectrum will be too narrow to see.
But of course actual absorption spectra do show up.

How come?

Title: Re: width of absorption lines
Post by: Borek on October 24, 2010, 04:30:20 PM

Heisenberg and Doppler.

Title: Re: width of absorption lines
Post by: nigel433 on October 25, 2010, 09:12:55 AM

ok :

- so the "Heisenberg" answer is that the energy jump is NOT completely sharp.

- "Doppler" seems to refer to shifts of observed spectra; not what I was considering,
   however.