Excitation of electrons by electromagnetic source

[Northprairieman]

If you hit a bound electron with a photon corresponding to that electron's ionization energy, you ionize the electron. What if you hit the electron with a photon with less energy? Will the photon still add its energy to the electron? Will the electron re-emit the photon with less energy?

Do you always need the exact amount of energy in a photon to excite an electron to a higher orbital? Can you say hit an electron with 2 photons of less energy to raise it to the same orbital as would be done by a photon with the exact energy of the next orbital?

 

[Northprairieman]

nevermind, I found what I was looking for.

https://en.wikipedia.org/wiki/Two-photon_absorption

 

[Simon Bridge]

If you hit a bound electron with a photon corresponding to that electron's ionization energy, you ionize the electron.

Atoms may be ionized, not fundamental charges. A photon carrying the appropriate energy or higher may ionize an atom by ejecting an electron.

What if you hit the [atom] with a photon with less energy?

If the photon energy is close to an energy gap, then the photon may be absorbed, an electron is promoted to a higher energy state and we say that the atom is "excited" - otherwise the photon just scatters.

Do you always need the exact amount of energy in a photon to excite an electron to a higher orbital?

Yes - though IRL there is no such thing as "exact".
This is why the absorption spectra lines are so precise. The width of the lines is usually more to do with the spectrograph than the atoms.

Can you say hit an electron with 2 photons of less energy to raise it to the same orbital as would be done by a photon with the exact energy of the next orbital?

No. Not commonly. If they did, think what the effect on the absorption spectra would be.

[edit] well done
Notice that the article talks about molecular excitation not atomic excitation - which is what you asked about. In general, wikipedia is a poor place to learn science.

 

[Simon Bridge]

Better sources for multi-photon absorption
http://webphysics.davidson.edu/alumni/jimn/final/pages/finalmpa.htm
http://cua.mit.edu/8.421_S06/Chapter9.pdf