Re: Photons-atoms interactions

From: Orcinus Orca (orcinus_orca_at_hotpop.com)
Date: 11/12/04 

Date: Fri, 12 Nov 2004 19:11:03 +0000 (UTC)

lordshiva5753@rediffmail.com (Kumar) wrote in message

> Thanks for nice reply.

No problem! :)

> It appears from your reply that 'photons of any
> energy can be absorbed by any atom & more phtons may be required for
> orbital shift to next higher level.

Yep, photons of any energy can be absorbed, reflected, or simply
travel through atoms (providing they donīt hit the nucleus). Iīm no
expert but I understand that a substance that is transparent does not
absorb or reflect photons to any significant degree.

I donīt think of orbital shift in terms of number of photons, I think
of it in terms of how much energy is supplied in a given interval of
time. This energy can be in the form of light, electricity, heat, etc.
So lets say that an electron of a given atom requires 10 units of
energy in one second to climb to a higher orbital. If you use photons
of low energy such as red light, you might need 1000 photons/s for the
shift whereas if you use photons of high energy such as ultraviolet,
100 photons/s might do. Yet you must keep in mind that a minimum total
amount of energy is required in a unit of time to excite the electron
to the next orbital. In other words, you can keep a light bulb on all
day directly over a nickel coin and the coin is never going to emit
light simply because the amount of energy given off by the light bulb
in a unit of time is not enough. The coin will get rid of that "low
density" incoming energy simply by getting warm and giving off that
heat.

> What will happen is some photons
> of lesser energy than minimum requred for orbital shift is absorbed?

The atom will warm up and give off heat. If it heats up enough, it
might emit light but the temperature required is usually high (like
that of a flame).

> Will that atom keep/store this lesser energy & atom will remain some
> excited (metastable state as indicated)till it gets more energy?

Sorry, never heard of metastable state. Iīm a chemist, not a
physicist. Besides, I graduated ages ago. :) No atom will store energy
as energy can always be dispersed. Energy is dispersed in many ways
such as light, heat, electricity, chemical reactions, etc. Energy is
like ions in a solution: it undergoes "osmosis", that is, it always
goes from where it is more concentrated to where it is less
concentrated. This is why the "energy concentration" to make an
electron climb an orbital needs to be higher than what the atom can
disperse otherwise.

After writing the last post, I refreshed my memory with some reading.
The wavelength of the photon emitted is equal to the distance between
the orbital of higher energy and the original orbital. That distance
is unique for every element although the same element can emit photons
with different wavelengths. It depends on how many orbitals an
electron climbs up then down which is directly related to how much
energy per unit of time is being supplied. If the amount of
energy/unit time is too high, the electron is simply ripped off the
atom (ionization as mentioned earlier).

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