Re: Photons-atoms interactions

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

Date: Thu, 11 Nov 2004 09:33:49 +0000 (UTC)

Igor Khavkine <k_igor_k@lycos.com> wrote in message news:<pan.2004.11.07.19.47.05.101066@lycos.com>...
> On Sun, 07 Nov 2004 13:44:56 +0000, Kumar wrote:
>
> > I want to know about Photons-atoms interactions as under:-
> >
> > 1. Whether emitted photons from any atom will be exactly similar & with
> > same energy as of absorbed photons?
>
> Any photon that can be absorbed can also be emitted. This is required for
> the interaction Hamiltonian to be hermitian.
>
> > 2. Can atoms remain excited for long? I mean if atoms absorb any photon,
> > can it remain excited for long with out emitting photon?
>
> This depends. If there is a large gap between the energy of the excited
> state and the next lowest energy accessible state, atom will decay to a
> lower energy state pretty quickly: (Delta T) ~ hbar/(Delta E). If, on the
> other hand, there is a bunch of closely spaced energy levels, if the atom
> is excited into one of these states it may stay there for quite a while,
> just oscillating between the different energy levels near by. These are
> called metastable states.
>
> > 3. If any substance, say stone piece, is divided into two pieces & those
> > two pieces are kept as some distance seprately. In consideration of
> > 'energy is to be corresponded for photon-atom interactions, If one piece
> > of stone is excited or vibrated--will it effect 2nd piece of that stone
> > kept at some distance?
>
> Electromagnetic interaction between neutral macroscopic objects are
> usually negligible. If they are very far apart, they won't feel each
> other. If they are close enough, they will experience van der Vaals
> attractive forces. If they get even closer together, you have to consider
> the atomic interactions between the surfaces more seriously.
>
> Hope this helps.
>
> Igor

Thanks for reply. You said, any photon can be absorbed & emitted. Do
you mean to say any photon with any energy lavel can be absorbed by
any atom or if there are some limitations to it?

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