Correct me if I am wrong, but atoms emit photons when they jump energy

[chug.-.chug]

Correct me if I am wrong, but atoms emit photons when they jump energy levels. Right?

 

[emily(:]

yes they do
(:

I think...

 

[pzona]

Depends what you mean by jump (also, it's the electron that "jumps" energy levels). An electron needs to absorb energy to increase its energy level. It can do this by absorbing a photon; so if by jump, you meant increase, then no, that would not be correct.

Think of it this way: if an electron goes to a higher level, it needs to gain some energy to do so. It can do this by absorbing a photon. If it goes to a lower level, it loses some energy, which is emitted as a photon.

 

[Ygggdrasil]

There are also non-radiative pathways (i.e. pathways that do not involve the absorption/emission of photons) for electrons to transition between different energy levels. For example, an electron can relax from an exited state to the ground state by releasing the energy as heat which gets transferred to surrounding molecules.

Electrons can be excited in non-radiative means as well. For example, an excited molecule (let's call it the donor molecule) can interact with an unexcited molecule (let's call this the acceptor molecule). Through a process known as resonance energy transfer, the energy from the excited electron in the donor can be transferred to the acceptor molecule. In the end, the donor molecule goes from the excited state to the ground state while the acceptor molecule goes from the ground state to the excited state. This process does not involve the emission of a photon by the donor and subsequent absorption of the photon by the acceptor (we know this because experiments show that resonance energy transfer from the donor to the acceptor occurs on a faster timescale than the emission of a photon by the donor).

Now, here's the caveat: the original process asked about atoms specifically. The processes I mentioned above occur mainly in molecules and many rely on properties specific to molecules (as opposed to atoms). I'm not sure if there are non-radiative excitation/relaxation processes that occur for atoms.

 

[alxm]

Now, here's the caveat: the original process asked about atoms specifically. The processes I mentioned above occur mainly in molecules and many rely on properties specific to molecules (as opposed to atoms). I'm not sure if there are non-radiative excitation/relaxation processes that occur for atoms.

That's pretty easy if you think about it.. A single atom has no vibrational or rotational degrees of freedom,
only its electronic and kinetic energy, and obviously it can't spontaneously accelerate or decelerate without emitting something.

Or to look at it another way: The electrons have a zero (expectation value) momentum before and after the transition,
so there's no momentum they can transfer to the nucleus. When a photon is emitted, the photon's momentum comes from the recoil of the atom.

 

[chug.-.chug]

Thank you for all the help and I apologize for the late reply (been busy).