[poor mystic]

Hi People
Imagine an atom being excited by a photon.
The photon is a little bit more energetic than is required to lift the the electronic state of the atom to its next level of excitement, but not energetic enough to go beyond that to a higher level.
When the atom has been excited to its first allowable level, there must be some energy left over.
What happens to that "extra" energy?

[Borek]

Are you sure atom gets excited by the photon of 'wrong' energy?

[poor mystic]

Thanks for your reply Borek
 I sure that the photon which excites the atom is often more energetic than would be required purely to raise the energy of an electron 1 step.
Consider the ground state of the Hydrogen atom for instance - the smallest quantum of energy is required to raise the single electron to its first level, but most of the photons likely to interact with the atom are much more energetic than that. Therefore there must sometimes be energy left over from such an interaction.

[KyleH]

I feel that your wording is wrong here poor mystic.  The ATOM does not get excited, it is the ELECTRON that gets excited.  Yes, the electron does absorbs the photon's light energy and get bumped to a higher energy level.  I would recommend looking into the Absorption Spectrum, and Emission Spectrum.  Googling them and reading the first few articles will probably answer your question. 

To get you started:  electrons absorb specific frequencies of light, which *Ignore me, I am impatient* them to the next energy level or higher.  If the frequency of light does not match the frequency of the atom's electrons, then the electrons will not absorb the light and nothing will happen to the electron, or the light frequency.

[poor mystic]

Thank you for your reply KyleH
According to your second paragraph, "If the frequency of light does not match the frequency of the atom's electrons, then the electrons will not absorb the light and nothing will happen to the electron, or the light frequency."

There remains some doubt in my mind as to whether this is true. I am particularly mindful of the phenomenon of fluorescence, where a high energy photon is absorbed and a lower energy photon re-emitted. In fact I had expected that the reply would be that the difference in energies between the photon and the quantum step of the electron must be re-radiated as a lower-energy photon. However the texts I have seen seem not to describe this question.
Hence my question on this forum.

[FreeTheBee]

If the matching energy/frequency would be merely a lower limit, would you then see peaks in for example a UV-VIS spectrum?

[poor mystic]

Thank you all very much for helping me with this question. When I am King you shall all be knighted.
I am still unsure about 1 matter.

"A laser emits single-frequency light. How is this light absorbed in the absence of atoms of the same sort that emitted it?"

[KyleH]

@Free the Bee, yes eventually the energy change is too big to be seen on the visible spectrum and the energy is then released in the form of uv and infrared rays.

Poor Mystic could you rephrase your question so I can try to answer it, I'm having a hard time understanding the wording aaha

[poor mystic]

Rephrased question: Using a ruby laser as an example.

A ruby laser emits a light which is unique to chromium atoms. When the laser is directed onto a block of carbon, say, I have heard that the carbon gets hot.
I always explained this to myself as the result of electrons absorbing energy and so changing chemical bonds.

In this thread I have learned that the exact amount of energy (quantum) contained in a photon can only be absorbed by an electron which is configured to receive that quantum of energy. There is never any energy "left over" to be disposed of.

As far as I know, the quantum series associated with any element is unique to the element.

Then unless there are chromium atoms in the carbon block, there can be no electrons excited by the laser. How, then, is the energy absorbed?

[KyleH]

It is the physical structure of the carbon block and the chromium block that determines whether or not the photons are to be observed.  It's not as if a light is travelling through a substance and says "this is a chromium electron, is should absorb me."  It is the way the atoms are structured that affect their properties and which light wavelengths they absorb.

This is why you can see some elements with similar absorption/ emission spectra.

Therefore it is reasonable to conclude that the carbon block is actually absorbing that frequency of light because it's electron configuration may be similar to chromiums.

HOWEVER, you also said the block gets hotter, I am not an expert, but nothing I have learned about has ever mentioned any change in temperature. Though it does make some sense because the electrons will vibrate quicker and release energy. I was always under the impression that the electrons emitted the same frequency of light it absorbed seen on the emission spectrum. 

In short, I would say that there may be something else beyond my knowledge going on when the ruby laser interacts with the carbon, but an educated guess of what could be occurring is my answer stated above.

[Borek]

When you heat block of carbon these are not electrons that get excited, but the lattice. And while energy stored in lattice is quantized as well, if the lattice is large enough (which probably means just thousands of atoms) it can behave as if the energy levels were continuous.

I can be wrong here, as my memory is blurry on the subject. In some particular situations it is possible for a molecule to absorb energy from the photon that is not of the correct wavelength. Excess energy is then either emitted or changed into kinetic energy. That how Raman scattering works.

[poor mystic]

Hello and thank you very much for your illuminating responses to my question.

It cannot surprise you that I find that the answers to my questions have raised more questions... it doesn't surprise me either.

I must treat these questions of the material world lightly, lest I forget my real interest. Yet curiosity is part of my life; I find it is fun to learn and wish I had 10,000 years to spend in such study.

I'm sure I'll someday have another simple-seeming question for the forum... until then I wish you all the best and the sweetest.

"poor mystic"