Re: Photons-atoms interactions

From: Kumar (lordshiva5753_at_rediffmail.com)
Date: 11/16/04 

Date: Tue, 16 Nov 2004 08:56:44 +0000 (UTC)

Igor Khavkine <k_igor_k@lycos.com> wrote in message news:<pan.2004.11.13.00.56.43.144164@lycos.com>...
> On Fri, 12 Nov 2004 19:09:22 +0000, Kumar wrote:
>
> > Caroline,
> >
> > Thanks for reply. Other posters have informed that "metastable state" is
> > possible. This indicate that absorbed & emitted energy can be differant
> > from each other, but emitted energy will normally always be the same or
> > its wavelength will always be same.Also, atoms can be kept in excited
> > state for long. I can't say for sure, but these metastable states can
> > somewhat represent "potential energy" or trapped/resting energy. What are
> > your comments?
>
> It is very easy for an atom to emit a photon that is of different
> frequency than what it absorbed. Consider the Hydrogen spectrum. It is
> given by photon energies of the form (1/n^2 - 1/m^2) Ry, where Ry is the
> Rydberg energy scale. Hydrogen atomic states are labeled by an integer n,
> and their energies are Ry/n^2. So when an electron jumps from one atomic
> state to another, we see a photon emitted whose frequency is part of the
> Hydrogen spectrum. If, to see a photon resulting from a jump from level n
> to level m, we had to excite the Hydrogen atom with a photon of exactly
> the same frequency, then spectroscopy experiments would have been
> impossible! Some frequencies of light can only be obtained as emission
> from certain transitions of certain atoms.
>
> Here's a caricature of what's going on
>
> Excited state
> with energy E1
> ----------------
> ^ | Photon of energy E1-E2
> | | ~~~~~~~~~~~~~~>
> Photon | |
> ~~~~~~~> | | Excited state
> energy E1 | V with energy E2
> | ----------------------
> |
> |
> | Ground state
> ---------------------------------
>
> Of course, the electron will not stay in the state E2 very long either.
> Some time later it may emit a photon to go to yet a lower excited state,
> or to go back to the ground state directly. There are many different ways
> for an excited atom to get rid of some energy, and the probabilities of
> these different processes can be calculated.
>
> Igor

Igor, Thanks for nice explaination. But what about metastable states.
Suppose an atom is excited in between Ground state & E1 state(if it is
possible & provided E1 level is first next shell than the ground
state). It can't emit photon specific to that atom. How then this atom
will get rid of this extra absorbed energy?

Is it so that; absorbed energy which do not match with the emission
levels as specific photon to that atom is relesed as Mechnical
waves(sound)>>Heat>>(photons if more energy is added)?

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