light emmitance by an atom

[karmapunk21]

let's suppose i had an atom A with the following properties:

has 2 electrons (therefore, only the first energy level is filled)

Energy between electron energy levels:
1-2 = 1j
2-3= 2j
1-3 = 3j

Now, if i were to focus 2 beams of energy, probably through a laser, one with a energy output of 1 j, another with an energy output of 2 joules, the electron on the first level will jump to the second, then to the third. My question is, when i no longer emit energy, will the electron drop strait from level 3 to level 1, emitting a photon with higher energy than either laser, or will the electron drop from level 3 to 2 to 1, thus emitting the same photons that it was struck with?
What conditions would result in the electron going from level 3 -> level 1 as opposed to level 3 -> level 2 -> level 1?

thanx.

 

[Shalmanese]

some electrons jump from 3 -> 1 and some jump frm 3->2->1. Im not sure about what the distirbution between the two is.

 

[Geniere]

I?ve not heard of the unit joule being used with the energy of light as it is such a large unit. I believe physicists normally use KeV (kiloelectron volts). 1Kev=1.60219e-010 nanojoules. A gamma ray is a very energetic photon as would be emitted by a star going Nova or a result of the BIG BANG. Gamma rays have energies of 100KeV and above. Photons below that energy would be X-rays, ultra-violet, visible, infra-red, radio?

A laser is a source of mono-chromatic (one color and wavelength), coherent light. It is the wavelength of the emitted light that determines the energy of a given photon. The intensity of the light, meaning the number of photons or brightness of the beam has nothing to do with the energy of a specific photon exiting the laser. Stated another way, it is the frequency of the light that determines its energy.

As to your basic question, re: the interaction of a photon and an electron bound to an atom:

A bound electron can only absorb an photon having a specific energy (meaning specific wavelength). If we assume the electron is at the lowest energy state (ground state), and does absorb a photon having the correct energy, it will be acquire more energy and no longer be at the ground state. It will remain in this more energetic state for a brief time after which it will emit a photon of the same energy that it absorbed. If the electron was not initially at the ground state, it must emit more than one photon to return to the ground state.

This interaction between electrons and photons is addressed by a theory called ?Quantum Mechanics?. If your interested in the subject, a must read is QED written by Feynman.

Regards

 

[karmapunk21]

Originally posted by: Geniere
I?ve not heard of the unit joule being used with the energy of light as it is such a large unit. I believe physicists normally use KeV (kiloelectron volts). 1Kev=1.60219e-010 nanojoules. A gamma ray is a very energetic photon as would be emitted by a star going Nova or a result of the BIG BANG. Gamma rays have energies of 100KeV and above. Photons below that energy would be X-rays, ultra-violet, visible, infra-red, radio?

I was using joules for the sake of simplicity, a placeholder for just "unit of energy," a purely theoretical value.

Originally posted by: Geniere
A bound electron can only absorb an photon having a specific energy (meaning specific wavelength). If we assume the electron is at the lowest energy state (ground state), and does absorb a photon having the correct energy, it will be acquire more energy and no longer be at the ground state. It will remain in this more energetic state for a brief time after which it will emit a photon of the same energy that it absorbed. If the electron was not initially at the ground state, it must emit more than one photon to return to the ground state.

In regard to the last sentence, that implies that if an electron jumps from 2->3 then from 3->1, then it must release more than 1 photon, correct? I understood that the jump from 3->1 would actually result in just 1 photon being released, but that photon has greater energy than the photon absorbed to make the electron jump from 2->3...

 

[Geniere]

Not being a physicist, I can only answer as to my understanding of electron-photon interactions. Another thing to remember is that free electrons behave differently than those quantum coupled to a proton (an atom). It is also better to think in terms of a hydrogen atom, as it has the least possible quantum states and only one electron to consider.

As I understand it:

A hydrogen atom?s electron exists in the ground state. It absorbs a photon of the proper energy and then exists in the next highest energy state. While it is in the excited state, it absorbs another photon that I believe would need to be of higher energy than the first photon. The electron now exists at the third possible quantum state. It emits a photon and returns to the second possible quantum state. It then emits a photon of a different energy to return to the ground state. It would be a continuation of this process through many energy states that yields the characteristic emission or absorption spectrum of the hydrogen atom.

Hopefully that?s close to the truth.

Regards

As I think about it, I believe it might happen that an electron may jump from 3 to 0 by emitting a photon having he total energy of those required to make two individual jumps, and similary when going from 0 to 3.

 

[MadRat]

One day you should build me an anti-atom made up of anti-matter particles and do the same expiriment, perhaps with the same process using the antimatter the anti-atom would absorb photonic energy?

 

[RossGr]

Originally posted by: MadRat
One day you should build me an anti-atom made up of anti-matter particles and do the same expiriment, perhaps with the same process using the antimatter the anti-atom would absorb photonic energy?

Humm.... All atoms, anti matter or not, adsorb "photonic" energy.

That is the fundamental process of elevating electrons to an excited state, essentially all photons are destined to be adsorbed by an atom.

 

[Fencer128]

In the simple monatomic system you present where there are 3 levels the only influences on whether an excited electron moves 3-2-1 or 3-1 are probabilities deriving from quantum theory. So it is impossible to say what way the electron would go - only that it has a probability of taking either route that can be quantified.

For a "real" system, it depends on the atom/crystal/molecule.

There are possible recombination centres. Recombination centres (such as positive ions (for electrons) in a doped semiconductor) with energy levels between the valence and conduction bands/levels of the semiconductor have a probability of "capturing" an electron as it relaxes. This would mean the electron could move straight from conduction to valence band or via the recombination centre. Again in comes down to quantum probabilities. In complicated structures there are also radiative and non-radiative recombination mechanisms. So such relaxation could occur with/without phonon emission. It all gets a bit complex!

Hope that helps,

Andy

 

[MadRat]

Originally posted by: RossGr

Originally posted by: MadRat
One day you should build me an anti-atom made up of anti-matter particles and do the same expiriment, perhaps with the same process using the antimatter the anti-atom would absorb photonic energy?

Humm.... All atoms, anti matter or not, adsorb "photonic" energy.

That is the fundamental process of elevating electrons to an excited state, essentially all photons are destined to be adsorbed by an atom.

But antimatter doesn't have electrons.

 

[f95toli]

There are "anti-electrons", these are known as positrons.
You can actually make "anti-hydrogen" and I remember hearing something about "anti-helium" beeing produced.

 

[Shalmanese]

A photon being elevated from 1->3 CAN jump 3->2 and 2->1.

An easy way to prove this is to simply look at the spectral emmision lines of a chemical. Assume a hypothetical atom with 1 electron and distinct energy levels g, e1, e2 and e3. If you look at the spectral emmision lines for this element, you will get the e1, e2 and e3 lines you expect but you will ALSO get a e3-e2, e3-e1 and e2-e1 line which are results of it jumping down in more than one stage. However, I am not sure of what the relative INTENSITY of these lines will be, I am sure that they will exist.

 

[MadRat]

Originally posted by: f95toli
There are "anti-electrons", these are known as <EM>positrons</EM>.
You can actually make "anti-hydrogen" and I remember hearing something about "anti-helium" beeing produced.

I'm willing to bet that anti-matter behaves in a contrast to normal matter when the positrons become excited.

 

[Shalmanese]

An anti-hydrogen should have the exact same emmision spectra as a hydrogen atom. Energy levels are indepentdant of charge.

 

[f95toli]

Originally posted by: Shalmanese
An anti-hydrogen should have the exact same emmision spectra as a hydrogen atom. Energy levels are indepentdant of charge.

True, one reason why making "anti-atoms" is interesting is to see if they in any way behave differently from normal matter. if they do it would contradict current theories. So far nothing "strange" has been observed.

 

[rjain]

If you look at some chemistry textbooks, you'll notice that when they describe spectra, there are groups called Balmer lines and other stuff (I forget the names for the others). They are grouped by which lower energy level the electron falls to when emitting that photon.

One group is for levels 2, 3, etc falling down to 1, another is for 3, 4, etc falling down to 2, etc. So all the different possibilities will happen, and the relative probabilities are a simple problem as far as quantum mechanics goes. (Not that I could figure it out, but I know just enough to know how to approach the problem.

The actual energy differences (for SINGLE electron systems only!) are proportional to the difference in the inverse squares of the energy levels involved. That is, kZ^2(1/a^2 - 1/b^2) where k is some constant of the strength of the electrical attraction and Z is the nuclear electrical charge (which determines how strong the electrical field is) and a and b are the two energy levels involved. Use Planck's constant to convert that energy into a frequency for the radiation.

 

[karmapunk21]

"A photon being elevated from 1->3 CAN jump 3->2 and 2->1."

Yes, but is the inverse true, thats what i'm asking. can a photon being raised 1->2->3 drop from 3->1?

Btw, thanx everyone for all their replies. I didnt expect so many responses!

 

[MadRat]

Originally posted by: f95toli

Originally posted by: Shalmanese
An anti-hydrogen should have the exact same emmision spectra as a hydrogen atom. Energy levels are indepentdant of charge.

True, one reason why making "anti-atoms" is interesting is to see if they in any way behave differently from normal matter. if they do it would contradict current theories. So far nothing "strange" has been observed.

What has been observed? I've heard of no anti-atom research as of yet.

 

[Shalmanese]

Well, there is currently facilities with "mass" production of anti-matter. Mass production being defines here as around the order of 100 atoms per day. So far, nothing exciting has been found except the posibility that anti-muons decay slightly faster than muons which might be the solution for why matter exists but anti-matter does not.

About the 1->2->3. First of all, Im not even sure that can happen often enough to be significant although, on reflection, it must since absorption spectra show lines on the 2->3. Im guessing it should. An easy way to test would be to simply shine two properly tuned laser through a solution and see the resulting spectral lines.

 

[MadRat]

I was under the impression that these facilities are creating anti-particles and not anti-atoms.

 

[sao123]

Unfortunately the real answer is not as cut & dried as you want.
Your question sounds good in theory, but for all practical purposes...what really happens is both.

If you had exactly one atom with a continuous laser beam (doing the calculus, however short your burst of laser is, its still continuous over an interval longer than the electron excitement period). The electron will repeatedly jump from level to level and back instantaneously. (the electron does not just stay excited forever until the energy is removed.)

1st - the probability is low that the same electron will be excited twice, by both lasers. Most of the time, the two joule laser might excite both electrons 1 step. However due to the number of times the electron will jump and return in a few seconds, everypossible combination will occur. In essence, both return paths will be used.

However, no matter which excited state you achieve and return from and which path, the color of the photon you see is determined by the wavelength of the electron you excited, not the number of joules applied, or the color of the laser energy applied before.

Thats why each element emits a its own single color when its excited by any different amount of energy. Neon will emit red regardless of whether you hit it with X joules, Y joules or Z joules, Which could excite electrons 1,2,3 steps and use any return path.

 

[f95toli]

Originally posted by: MadRat
I was under the impression that these facilities are creating anti-particles and not anti-atoms.

Anti-atoms ARE anti-particles.
Anti-hydrogen us just an anti-proton+a positron. Anti Helium-4 is just an anti-alpha particle+2 positrons.

 

[rjain]

Recently, the first particles of anti-hydrogen were created. I don't know how long they managed to last or what observations were made.

 

[rjain]

Transitions from 2->3 and 2->1 and 3->1 are definitely possible and do occur. An electron in energy level 3 is an electron in energy level 3. It has no "memory" of how it got there.

 

[MadRat]

Originally posted by: f95toli

Originally posted by: MadRat
I was under the impression that these facilities are creating anti-particles and not anti-atoms.

Anti-atoms ARE anti-particles.
Anti-hydrogen us just an anti-proton+a positron. Anti Helium-4 is just an anti-alpha particle+2 positrons.

I guessing neither stay together long without a neutron. The stable forms of natural helium and hydrogen have neutrons, right?

 

[rjain]

The most common form of Hydrogen has no neutrons. Deuterium is a proton + neutron + electron.

An alpha particle is 2 neutrons + 2 protons. 2 protons alone are quite unstable, yes.