Photon Question

[Little Bang]

If we had an evacuated tube that has an injector at each end capable of injecting a molecule from each end such that the two molecules are on a collision course. When they collide the energy of their collision would create a photon having an energy exactly equal to that of the collision?

[Erasmus00]

If we had an evacuated tube that has an injector at each end capable of injecting a molecule from each end such that the two molecules are on a collision course. When they collide the energy of their collision would create a photon having an energy exactly equal to that of the collision?

 

It depends a lot on the specifics. If you collide down your system say, a positron and an electron then you would get some photons and maybe other particles depending on how fast they were moving. Neutral particles would most likely result in an elastic collision.

 

Charged particles would emit a photon, but the particle won't come to a dead stop but rebound. Hence, not all of the energy will be carried by photons.

-Will

[Little Bang]

Will, you have not answered my question. Will a collision between two molecules produce an infrared photon?

[Erasmus00]

Will, you have not answered my question. Will a collision between two molecules produce an infrared photon?

 

I did answer. To reiterate If the particles are neutral, then no. If the particles are charged they will spit out a photon, but the energy will NOT be equal to their total initial energy. The atoms still move after the collision. The exact energy of the photon depends on the specifics.

-Will

[Little Bang]

Your saying that the collision of two neutrons will not produce a photon regardless of how much energy is involved in the collision?

[Qfwfq]

Molecules also have a helluvalotta internal degrees of freedom.

[Erasmus00]

Your saying that the collision of two neutrons will not produce a photon regardless of how much energy is involved in the collision?

 

I'm saying at normal energy, the neutrons won't produce a photon. At extremely high energies, I imagine you could get some effects to create some photons because the quark structure probably becomes important.

 

Again, your question is extremely vague. If you want better answers, please add some specifics to the question. What particles/molecules do you want to use? What kind of energies? Do the particles have the same energies? What is the cavity made of? If the cavity is conductive, is it close enough to the molecules to couple to any charged particles?

-Will

[Qfwfq]

I'm saying at normal energy, the neutrons won't produce a photon. At extremely high energies, I imagine you could get some effects to create some photons because the quark structure probably becomes important.

Actually, apart from the complication of accelerating a neutron, at high energy you would easily get hadronic diffraction which means a helluvalotta stuff will be produced, more than just a photon or two.

[cwes99_03]

Yah, Will is looking at a very low energy case.

Any interaction between any two molecules with sufficient energy will produce something. Now, if the total amount of kinetic energy remains the same in the particles and no mass is lost, then no light is created (in any part of the spectrum).

Most light is created when an excited electron changes between two orbitals (states). The collision may excite an electron which then quickly gives up its new found energy and that would result in light being produced, however, it would also result in a change of total energy of the two molecules that colided so as to conserve the laws of physics.

[Little Bang]

I guess what I am trying to find out is the specific conditions that create a photon. Is it true that they only happen in the collision of charged particles, and I'm not referring to relativistic collisions because those produce almost everything?

[cwes99_03]

No. While the collision of charged particles may produce a photon, no collision is needed. All that is needed is for a particle with electrons to pass through a sufficient electric field to excite one of the valence electrons to change down an energy state. The type of light produced is equal to the difference between the energy states before and after the transition (at least as far as low end spectrum light production goes). To produce higher levels of light radiation (such as gamma), generally an atom has to be split to release enough energy.

 

However, two colliding particles that aren't perfectly elastic will also produce light (which maintains the energy balance before and after the collision.)

 

Check out the Raman Effect for more information on how light interacts and is produced with particles. It is only a tiny part, but I think it will show you that there are lots of different ways for light to be produced.

[Qfwfq]

It depends on what one means by the word 'collision'. In modern terminology, any interaction that isn't between two particles in a bound state. Of course, even in a bound state there are virtual bosons...

[Farsight]

I guess two magnets can "collide", and interact without actually touching each other.

[Erasmus00]

All that is needed is for a particle with electrons to pass through a sufficient electric field to excite one of the valence electrons to change down an energy state.

 

It depends also on what you mean by particle. I was thinking of fundamental particles, (protons, neutrons,electrons) which take high energies to excite their substructure. Also, in the absence of any field in the tube, the electrons aren't going to be excited by anything but the field of the other atom, i.e. a collision.

-Will

[cwes99_03]

Quite right, I think I latched on to the use of the word molecule in the original question.

[Little Bang]

If we look at the reaction of hydrogen with oxygen, there are photons produced I guess becase of the excitation of the valence electrons. Correct me if I'm wrong but that should mean that some mass was converted to a photon. Now we can use electrolosis to break the hydrogen and oxygen back apart. Does this mean that some energy has been converted into mass?

[cwes99_03]

What do you mean by reaction?

 

If you are talking about the chemical reaction between Hydrogen and Oxygen to form water, then I'd say this needs to be in the chemistry forum not physics and mathematics.

 

Also, if it should be moved to chemistry, you'll have to back up your claim about their being a photon produced.