Are photons a "part" of atoms.

[Sorcerer]

When a atom floresces an electron drops down an energy state and a photon is emitted.

 

Is it correct then to say that photon is a part of the atom? Is there any specific place it resides. Was it a part of the electron?

 

If it isn't a part of the atom and only carrying away energy, is there any preference in the process for which photon it embers? IE does it choose the nearest, ones travelling in specific directions etc over others?

 

If it is neither of these and the photon is created, where does the photons other property, spin come from?

[ajb]

Is it correct then to say that photon is a part of the atom?

Not really. You should think of the energy loss using a transition as 'kicking' the background electromagnetic field producing a photon. Of course I have been very loose here.

[Sorcerer]

Not really. You should think of the energy loss using a transition as 'kicking' the background electromagnetic field producing a photon. Of course I have been very loose here.

I used to be very comfortable thinking of it like this. But have had it driven into me on this forum that photons aren't energy, they have energy. They also have spin, how does that energy loss create the spin of the photon? And where does the spin go during absorbtion? Is there a spin/energy equivalency?

 

Can photons exist with 0 energy as dormant spin only?

Edited December 24, 2015 by Sorcerer

[ajb]

You still have all the conservation laws of total angular momentum. This is important in selection rules for electronic transitions..

[Strange]

If it is neither of these and the photon is created, where does the photons other property, spin come from?

 

Great question. I assume the spin of the electron must be 'flipped' but I don't know...

[Sorcerer]

 

What evidence is there which would falsify the hypothesis that energy is only transferred to the electron during absorbtion. While the photon, minus all but a non 0 amount continues. And emission is where a similar photon gains energy from the electron?

 

Is there any direction preferred in fluorescence. Eg are photons absorbed and emitted perpendicularly, tangentially etc. If we made direction a priority, would uncertainty over momentum hinder an experiment testing this?

 

While an electron is in an excited state, where is the photons energy located? Is it in the electron moving it away, or in the nucleus pushing it away?

[ajb]

Great question. I assume the spin of the electron must be 'flipped' but I don't know...

Thinking about the hydrogen atom in particular...

 

The spin of the emitted photon is 1 and so the angular momentum of the electron must change accordingly. The spin quantum number of the electron does not change.

[Sorcerer]

You still have all the conservation laws of total angular momentum. This is important in selection rules for electronic transitions..

So how does the spin of an atom differ post absorbtion, what subatomic particle holds the spin, does it matter? Are some forbidden, eg fermions and bosons are defined and grouped by their different spin types.

[ajb]

Is there any direction preferred in fluorescence.

I do not think there is any preferred direction in general.

 

While an electron is in an excited state, where is the photons energy located?

This is phrased awkwardly. The energy of the photon comes from the difference in the energy of the electron in the initial and final state.

So how does the spin of an atom differ post absorbtion, what subatomic particle holds the spin, does it matter? Are some forbidden, eg fermions and bosons are defined and grouped by their different spin types.

Basically, you need to take the photon's spin into account when looking at conservation of angular momentum.

[Sorcerer]

Fluorescence differs from phosphorescence in that the electronic energy transition that is responsible for fluorescence does not change in electron spin, which results in short-live electrons (<10-5 s) in the excited state of fluorescence. In phosphorescence, there is a change in electron spin, which results in a longer lifetime of the excited state (second to minutes).Fluorescence and phosphorescence occurs at longer wavelength than the excitation radiation.

http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Electronic_Spectroscopy/Electronic_Spectroscopy%3A_Theory

[ajb]

In phosphorescence, there is a change in electron spin...

Okay, but we must still have conservation of the total angular momentum.

[Sorcerer]

 

Where is the spin located for that brief time? Where does the photon "go"?

 

In the case of phosphorescence, is it wrong to view an excited electron as containing or being joined with a photon

If a photon had all its energy removed would it come to rest?

 

Would a photon with 0 energy at rest even be measurable?

[ajb]

Where is the spin located for that brief time? Where does the photon "go"?

I am not sure how to answer that. All we really know is that we have certain conservation laws, that is numbers that must balance before and after. It is not so clear what happens in between, but the mathematics of quantum mechanics handles all this.

 

 

In the case of phosphorescence, is it wrong to view an excited electron as containing or being joined with a photon

I do not think you should really think of the election itself as containing photons.

 

Well, in quantum field theory it becomes more subtle as we have the notion of bare and dressed particles. However, I do not think this really has much to do with electronic transitions.

[Sorcerer]

Can't photons themselves create electron positron pairs though? Intuitively I would view an electron then being made of photons, like a proton is made of quarks. I know QM isn't very intuitive, but how would saying this be wrong?

 

Also that wiki confuses me in the introduction. Saying after sodium absorbtion of 2 photons energy is emitted in all directions, how can 2 photons be emitted in all directions. And if more photons are emitted where does their spin come from?

 

Maybe by all they mean opposing directions? Or perhaps any direction, no specific direction?

 

And now I am thinking of everyday visible light reflection. Where does the spin go when a green plant uses that photons energy for photosynthesis?

[ajb]

Can't photons themselves create electron positron pairs though?

Yes, we have pair production.

 

Intuitively I would view an electron then being made of photons...

This is not what our theory or experiments suggest. There is no internal structure that we know of, let alone one we can explain using bound states of photons.

 

...like a proton is made of quarks.

But this is very different.

 

I know QM isn't very intuitive, but how would saying this be wrong?

It does not really sit well with our understanding of quantum field theory, nor really our experimental results on the structure of electrons.

 

 

Also that wiki confuses me in the introduction. Saying after sodium absorbtion of 2 photons energy is emitted in all directions, how can 2 photons be emitted in all directions.

I assume the article is talking about many such absorptions and emissions.

 

 

And if more photons are emitted where does their spin come from?

Again, we need to think about the conservation laws.

 

 

Maybe by all they mean opposing directions? Or perhaps any direction, no specific direction?

Being in opposite directions would imply conservation of linear momentum.

 

And now I am thinking of everyday visible light reflection. Where does the spin go when a green plant uses that photons energy for photosynthesis?

I assume into the total angular momentum of the electrons of the products.

[Sorcerer]

This is not what our theory or experiments suggest. There is no internal structure that we know of, let alone one we can explain using bound states of photons.

But electrons do have a measurable structure, with mass, energy and spin. Photons too have a dual structure, with energy and spin. Perhaps then energy and spin are the primary particle. Can one ever be found without the others presence? So like quarks (but yeah you're right not really at all) they can only exist paired. And like quarks they have a third interchangeable particle mass.

 

It does not really sit well with our understanding of quantum field theory, nor really our experimental results on the structure of electrons.

 

How would you design an experiment to look at an electron? Don't they absorb photons? If they're made of photons, isn't that like trying to look at a photon by reflecting another off it?

 

Anyway merry Christmas. I've got a nice brunch waiting. Damn this stuff is interesting though.

 

Thanks for the input.

[ajb]

But electrons do have a measurable structure, with mass, energy and spin.

That is not what is meant by internal structure. I mean that we see no evidence that the electron is made up of any constituents.

 

 

Photons too have a dual structure, with energy and spin.

Again this is not what we mean by internal structure.

 

Perhaps then energy and spin are the primary particle. Can one ever be found without the others presence?

Energy and spin are properties of particles (or fields). There is no notion of pure energy or pure spin.

 

 

So like quarks (but yeah you're right not really at all) they can only exist paired.

At the energies we have probed yes.

 

And like quarks they have a third interchangeable particle mass.

I don't quite understand.

 

How would you design an experiment to look at an electron? Don't they absorb photons? If they're made of photons, isn't that like trying to look at a photon by reflecting another off it?

There are methods of looking at the electron form factor, which is related to the charge distribution. In theory this should be 1 as electrons are modelled as point-like particles. The experimental bound on the electron radius is something like 10^-18m. So we know that up to that scale there is no internal structure seen.

[swansont]

 

Great question. I assume the spin of the electron must be 'flipped' but I don't know...

spin or orbital angular momentum, depending on the specifics of the interaction