Do just electrons emit photons?

[desta41]

Do just electrons emit photons/radiation. Or do atoms and molecules emit photons as well? Just can't get a clear answer on this.

And if atoms and/or molecules also emit photons, can you please explain what causes them to?

 

[Bystander]

https://en.wikipedia.org/wiki/Black-body_radiation

 

[desta41]

https://en.wikipedia.org/wiki/Black-body_radiation

Good information, but what I'm asking about is not covered there. I need a specific answer regarding whether molecules and atoms, themselves, emit photons. I know electrons emit photons, but do molecules emit them as well? And speaking of blackbody radiation, is that emitted from just electrons or from both electrons and molecules?

 

[mathman]

Radioactive (nuclei) decay leads to gamma ray production.

https://en.wikipedia.org/wiki/Thermal_radiation This describes lower energy sources.

 

[Bystander]

Re-read the part of the article on "cavity radiation."

 

[ZapperZ]

Do just electrons emit photons/radiation. Or do atoms and molecules emit photons as well? Just can't get a clear answer on this.

And if atoms and/or molecules also emit photons, can you please explain what causes them to?

If I take a bunch of protons and jiggle it up and down, I can generate light.

ANY accelerated charge will create EM radiation.

Zz.

 

[blue_leaf77]

I know electrons emit photons, but do molecules emit them as well?

I would say in most cases, the emission of photons always follow from some mechanism in which a change in energy of the atomic / particle system occurs - simply as a consequence of energy conservation. So, if atoms or molecules relaxate they will emit photons.

 

[desta41]

What about when a molecule rotates? Or the stretching of molecular bonds? Would those occurances cause radiation? Two things examples of molecules radiating (and not the electrons and protons as the cause)...

 

[sophiecentaur]

What about when a molecule rotates? Or the stretching of molecular bonds? Would those occurances cause radiation? Two things examples of molecules radiating (and not the electrons and protons as the cause)...

I thought a molecule was made up of electrons and protons? The actual energy of the photons depends upon the energy change involved.

 

[desta41]

I thought a molecule was made up of electrons and protons?

Yes, of course. I was just meaning the rotation and stretching of the molecule causing radiation. Not the charge from electrons or protons. Is radiation just caused from electrons and protons then? Not from rotating or stretching molecules?

 

[sophiecentaur]

Bending and stretching and rotating a molecule alters the arrangement of the electrons and protons - what else? Changing the arrangement of charges will involve radiation. Why would you think otherwise? It is a pretty consistent model.

I guess it's worth pointing out that a molecule that is rotating will only radiate (or accept) a photon if there is a permissible transition in its energy states. But that's the same as with an 'orbiting' electron.

 

[desta41]

When in an atom, I was caught into thinking that the electrons jumping down energy levels was just the cause of radiation. But makes sense, then, that bending, stretching, and rotating of the molecules leads to the electrons emiting photons.

So is blackbody radiation due more to the electrons continuously jumping down energy levels and therefore radiating photons, or from the aforementioned types of molecular movements causing the electrons to emit radiation? Or both?

 

[sophiecentaur]

When in an atom, I was caught into thinking that the electrons jumping down energy levels was just the cause of radiation. But makes sense, then, that bending, stretching, and rotating of the molecules leads to the electrons emiting photons.

So is blackbody radiation due more to the electrons continuously jumping down energy levels and therefore radiating photons, or from the aforementioned types of molecular movements causing the electrons to emit radiation? Or both?

You seem to insist on talking in terms of 'electrons'. This will be because, as with everyone else, you got The Hydrogen Atom in your introduction to QM. Whilst everything contains electrons, the way it works is not as simple as The Hydrogen Atom. The energy states in a single atom all involved relatively big gaps and will not involve all frequencies of radiation. With molecules and densely packed matter (solids and liquids) there are many more combinations of charges and you have to include everything in a model to describe how the radiation interacts with the system. It's to do with the states of all the charged particles in a molecule, relative to each other that explains the frequencies that are absorbed and radiated. In condensed matter, you don't have discrete levels but whole continuous bands of energy, which is why you get continuous spectra and not lines in a 'red hot' object.
Bottom line is that you need to not hang on to the simple models if you want to get to understand the more advance phenomena. For example, you cannot explain how light is reflected coherently from a shiny metal surface if you model it on one photon exciting one electron on the metal surface and then a photon being re-emitted. That would never produce a specular reflection because of the random delay in the absorption / emission process. It has to involve a large region of the surface, with gazillions of electrons involved.

 

[desta41]

I appreciate your expanding on this matter. I feel as if I have a better understanding.

So would it be fair to say, then, that, thermal radiation from an object (not from an ideal blackbody) has little or nothing to do with electrons jumping or changing energy levels in an atom? It would be all or mostly from rotation and vibration of molecules (which, of course, involves the altered arrangement of electrons and protons)?

Question #2: Let's take a brick in the sunlight. If you were to say that it's the molecules of the brick that absorb the photons, couldn't it be said that, technically, the electrons are absorbing them as well since the molecules contain electrons?

 

[ZapperZ]

I appreciate your expanding on this matter. I feel as if I have a better understanding.

So would it be fair to say, then, that, thermal radiation from an object (not from an ideal blackbody) has little or nothing to do with electrons jumping or changing energy levels in an atom? It would be all or mostly from rotation and vibration of molecules (which, of course, involves the altered arrangement of electrons and protons)?

Question #2: Let's take a brick in the sunlight. If you were to say that it's the molecules of the brick that absorb the photons, couldn't it be said that, technically, the electrons are absorbing them as well since the molecules contain electrons?

Unfortunately, this is a very common theme here in this forum, and it requires another explanation why we have such a field of study as solid-state physics and condensed matter physics.

When atoms and molecules are clumped together into a solid, they form a conglomerate in which the characteristics of the solid are predominately due to the collective behavior of all these atoms and molecules. What that means is that the individual behavior of the atoms and molecules are often no longer apparent in the properties of the solids.

One important emergent, collective property that a solid has that are not found in isolated atoms and molecules is presence of phonons. This is a vibrational modes of a solid due to the gazillion atoms and molecules that make up the solid. In fact, phonons are responsible for a large range of properties of the solid, ranging from optical to thermal to electric transport.

The reason I brought this up is because if you learn solid state physics, and especially the http://www.uni-tuebingen.de/meso/ssscript/phononen.pdf , you will discover that the phonon or vibrational modes have two branches - the acoustic and the optical modes.

The optical modes are "electromagnetically active". It is basically a dipole mode, and this mode can not only absorb EM radiation, but can also, under the right condition, emits EM radiation (it is often called Raman active). This property is often attributed to why we see colors from different objects.

So when you heat, say, a tungsten wire in an incandescent light bulb, if you look at the spectrum using the spectroscope that we give students in many intro physics laboratory, you will see a continuous spectrum of color, instead of a set of discrete lines that is expected from atomic transition. The heat causes all these vibrational modes of a solid to be enhanced to the point where the EM radiation they emit is intense enough to be seen. This is why the spectrum of light given off is different than from atomic gasses.

Moral of the story here: More Is Different (Phil Anderson)!

Zz.

 

[sophiecentaur]

couldn't it be said that, technically, the electrons are absorbing them as well since the molecules contain electrons?

You can say what you like. Your version has some aspects of truth in it. But if you insist on your particular, partial explanation then you will find it harder and harder to explain all the EM absorption and emission phenomena there are.
Instead of trying to hang on to your basic idea, seemingly at all costs, I recommend that you make an effort to learn a bit more Physics. Why do you come to PF if you just want to be 'right' all the time?

 

[desta41]

Unfortunately, this is a very common theme here in this forum, and it requires another explanation why we have such a field of study as solid-state physics and condensed matter physics.

I more than appreciate your response. I've heard, though, that a real-life blackbody (not an ideal or perfect one) will show spectral lines. And I've heard that some studies in astronomy use this kind of blackbody analysis--e.g. relative intensities and spectral lines--to infer information about stars. Perhaps I'm missing something big here. But, if I'm understanding you correctly, thermal radiation, from objects, would just involve molecular vibrations and not jumping of electrons? Or can it be both for when it comes to a non-ideal blackbody?

 

[desta41]

Instead of trying to hang on to your basic idea, seemingly at all costs, I recommend that you make an effort to learn a bit more Physics. Why do you come to PF if you just want to be 'right' all the time?

In no way am I trying to be right. I am just trying to get a full understanding and throwing some things out there for analysis. I really appreciate the long answer you gave me and I feel it has helped. Was just wondering about that one other way of looking at it, that's all.

 

[sophiecentaur]

And I've heard that some studies in astronomy use this kind of blackbody analysis--e.g. relative intensities and spectral lines--to infer information about stars.

I think you may be referring to the absorption lines, caused when the black body light emitted from a star shines through its outer atmosphere (rarified gas with single atoms or molecules where the energy levels are discrete). The Helium Lines were spotted in sunlight - for the first time and that was why the name Helium was chosen for the newly found element, or so I believe.
New phenomena need new ways of looking at things and the simple 'electrons radiate EM' approach is just not enough. Do a bit more reading round instead of endless Q and A, which can be very inefficient use of your time if you want the bigger picture.

 

[desta41]

I think you may be referring to the absorption lines, caused when the black body light emitted from a star shines through its outer atmosphere (rarified gas with single atoms or molecules where the energy levels are discrete).

Yes, thank you for clearing that up about absorption lines. And, I hear you about reading up more. Let me just close by presenting you one other thing.

What may have been confusing me in regard to whether it's the electron jumps or molecular rotations and vibrations causing the emission of photons is the following (received from an associate):
'In solids, liquids, and gases simple scattering of the molecules transfers the kinetic energy of one molecule to the potential energy of another, i.e. raises an electron to a higher level. The electron goes back to its ground state releasing a specific photon, or a cascade of photons, depending on the energy. Remember that the higher levels with respect to n, the radial quantum number, are closely packed. These photons are the ones emitted as blackbody radiation, and they are a continuum because of the 10^23 molecules per mole and the almost continuous energy levels.'

The part that says, 'The electron goes back to its ground state releasing a specific photon, or a cascade of photons', seems to contradict the idea of blackbody radiation and a continuum, and of molecular vibrations as being the cause for emiting.

If you can shed any light on that quote, I'd be more than grateful.

 

[sophiecentaur]

i.e. raises an electron to a higher level.

You really don't want to let this one go, do you?
Answer me this: A Hydrogen Atom consists of just one Proton and One Electron. When, in the simple, quasi-mechanical model, the electron is disturbed in its 'orbit', what happens to the Proton? Does it stay where it is? Relative to the centre of mass, if one moves in one direction, doesn't the other move in the opposite direction. Doesn't the proton count in this? You could say that, as the proton is 2000 times as massive as the electron, you can ignore it but there would be a finite effect.

It is the energy state of the whole system - molecule or lump of metal, that counts in all em/charge interactions. It is only in the simplest cases that your electron idea can be used as a near-enough model.

PF can answer your randomly directed questions till we are all blue in the face. Do you have access to any textbooks? You do not need "papers" to help you educate yourself because they will either be trivial and possibly incorrect or way over your head. What you need is to have the information presented to you in a suitable order to get a logical sequence of ideas that can give you some understanding. I know that plain reading is not fashionable but I can definitely assert that the only students of mine (A level) who ever got far in Physics were the ones who used their Text Books and read around. Many of the others would rather waste a lesson on misdirected questions because they enjoyed a chat rather than doing actual work. Personal models of QM are doomed to failure. (I think I may safely say).

 

[desta41]

I am definitely aware that it's the whole system. I was mainly trying to determine what the primary contributor to thermal radiation (of most objects) was: the electrons, as a whole, and their jumps, or the molecular vibrations and rotations with moving dipole charge.

 

[sophiecentaur]

Why are you drawing a distinction? In what real situation do you ever just get an isolated electron 'jumping'? Answer: When a free electron is buzzing around in a rarified gas and can be accelerated by an applied magnetic or electric field.
On other situations it is a bit more 'obvious' that there are other charged particles involved - i.e. a charge system and not an individual electron. Even in the first example, there has to have been some other charge involved to cause that event.
If you are talking of an 'object' you never have the situation of an isolated electron.

the electrons, as a whole, and their jumps

I'm not sure what you mean by this.??

 

[desta41]

I don't mean an isolated electron. I'm thinking of the massive amount of electrons that make up an object (say, a piece of wood). There, of course, would be billions of atoms making up the piece of wood, and would be a number of electrons in a good percentage of the atoms that make up the wood. I'm thinking how the electrons, when they absorb photons, become excited and jump to higher energy levels, then, how they release photons as they lose energy and fall to lower states. I'm thinking of all those electrons collectively and how those released photons would likely be considered thermal radiation.

I'm also thinking of the molecular vibrations and rotations of that piece of wood and the moving dipoles of the molecules and how this aspect contributes to emitted thermal radiation.

For each of the two types mentioned above (ways to emit thermal radiation), I'm looking at this in a collective sense; no instance of an isolated electron.

I hope you see what I'm trying to express.

 

[sophiecentaur]

You are asking for a description of the detailed energy levels corresponding to all the structures in a solid object. One thing I can be pretty sure of is that there won't be any rotation in a solid. It's already beenmentined that we are dealing with Solid State Physics here. You need to find out about that. Read a book and be prepared to do some Maths.

 

[desta41]

I know, a lot to study. I had wanted to add this as part of my last reply. I included two quotes from this wikipedia page: https://en.m.wikipedia.org/wiki/Energy_level -- they are discussing the three types of energy transitions for a molecule:'Electrons in atoms and molecules can change (make transitions in) energy levels by emitting or absorbing a photon (of electromagnetic radiation) whose energy must be exactly equal to the energy difference between the two levels.''Molecules can also undergo transitions in their vibrational or rotational energy levels.'What I get from this is, there are three types of ways photons or thermal radiation can be absorbed and emitted.

If I've assumed wrong, please let me know. But, yes, I will definitely be doing plenty of research as time permits.

 

[DrClaude]

Let me first repeat two very important points that were already mentioned. First, it is not the electron in an atom that absorbs/emits a photon, it is the combined system electron + nucleus. Because of the mass difference, the problem is often simplified by considering the nucleus to be fixed, such that only the motion of the electron is considered, but with the presence of the nucleus, there would be no net change of the state of the electron. Second, solids can't be viewed simply as a collection of atoms. Therefore, my answer below is valid for isolated atoms or molecules, or in the gas phase.

'Molecules can also undergo transitions in their vibrational or rotational energy levels.'

This is an oversimplification. At the very core of quantum theory, you can describe the overall state of the molecule, and consider transitions between those states. By introducing approximations, you can separate the electronic motion from nuclear motion (Born-Oppenheimer approximation), and consider electronic states independently from the motion of the nuclei. For the latter, you can make other approximations to separate the overall orientation of the molecule from the relative positions of the nuclei, hence separating rotation from vibration. But these are approximations. One thing that is important to note is that there is no such thing as a pure vibrational transition. Within a given electronic state, you have ro-vibrational transitions, where the rotational state changes at the same time as the vibrational state. The simple explanation for this is conservation of angular momentum: the photon has spin angular momentum, and thus the molecule must gain/lose that angular momentum when it absorbs/emits a photon. Pure rotational transitions are however possible. Likewise, since vibrational states are a subset of electronic states, an electronic transition is always accompanied by a change of vibrational state.

The splitting into three categories of transitions is also related to the fact that they are distinct spectroscopically. Electronic transitions are typically in the UV-Vis part of the EM spectrum, ro-vibrational in the infra-red, and pure rotational in the microwave.

For isolated atoms or molecules, these transitions appear at precise, discrete photon energies. But already in the gas phase, the presence of other atoms or molecules will shift the energy levels, for instance because of collisions or the Doppler effect. For high enough densities and temperatures, the absorption/emission spectrum becomes continuous.

 

[sophiecentaur]

It's also worth pointing out that the 'electron / photon' theory is based on the Bohr Atom model and that is more than a hundred years old. No surprise that it fails to explain a lot of phenomena that have since been dealt with.

 

[desta41]

it is not the electron in an atom that absorbs/emits a photon, it is the combined system electron + nucleus

Thank you so much for your in-depth answer. First off, regarding the above, do you mean that the combined system (electron + nucleus) absorbs/emits the same photon? And, when you say 'combined system', that would be similar to just saying 'atom' (or molecule)?

Likewise, since vibrational states are a subset of electronic states, an electronic transition is always accompanied by a change of vibrational state

And the rotational state would change at the same time as the vibrational state, correct (referring back to your mentioning ro-vibrational transitions)?

Second, solids can't be viewed simply as a collection of atoms

Could you expand on that?

Therefore, my answer below is valid for isolated atoms or molecules, or in the gas phase.

What about solids, liquids, and compressed gases? What would be the best descriptive (since they would likely all contain electronic, vibrational, and rotational states)? Would it be to just not consider any separations?

 

[Point Conception]

http://hyperphysics.phy-astr.gsu.edu/hbase/mod3.html#c3
Molecular translation. rotation and vibration correspond to absorption and photon emission in infrared part of EM spectrum . Also see infrared spectroscopy