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I know atoms or molecules will absorb a photon of the right frequency but will this change the charge. If you have a neutral molecule once it absorbs a photon will the charge change to a positive or negative. I'm thinking no but I'm not sure if an electron gets knocked off. Like the photo electric effect I understand photons do not carry charge. But they do raise the energy of an atom or molecule and I was wondering if it would raise the energy enough to knock an a electron out of its orbital or one of the covalent bonds changing the charge.

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  • $\begingroup$ "I know atoms or molecules will absorb a photon of the right frequency but will this change the charge." Photons do not carry electric charge so how could this be true? $\endgroup$ Sep 13, 2015 at 3:25
  • $\begingroup$ I understand photons do not carry charge. But they do raise the energy of an atom or molecule and I was wondering if it would raise the energy enough to knock an a electron out of its orbital or one of the covalent bonds changing the charge $\endgroup$
    – newguy
    Sep 13, 2015 at 3:31
  • $\begingroup$ newguy, then you're asking a different question. I recommend that you edit accordingly. $\endgroup$ Sep 13, 2015 at 3:42

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Charge is a conserved quantity. If the incoming photon on a molecule is of the appropriate energy , an electron can be kicked from a low energy level to a higher energy level .Since the charge of the photon is zero , the molecule remains neutral.

If the energy of the photon is high enough the electron gets kicked out, the molecule becomes positively charged by one unit. Depending on the material , the freed electron will fall back releasing a photon or as you say the photoelectric effect, may appear. The photoelectric effect is seen at the surface of metals , freed electrons coming out, because in metals the outer electrons of the molecules are collectively bound in energy bands and the probability of getting enough energy to get out of the surface by absorbing a photon , is high.

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  • $\begingroup$ How would you figure out what the energy level of the photon had to be to knock an electron out of a covalent bonds and if an electron is knocked out could you use a strong positive charge to draw it away from the molecule $\endgroup$
    – newguy
    Sep 13, 2015 at 3:46
  • $\begingroup$ You will have to research the literature on modeling molecules, whether the one you are interested in has been modeled and its energy levels studied and get the energy difference in order to free it. Otherwise you would have to do the job yourself, though you could estimate from similar molecules that have been modeled and play in the lab with close by photon energies. As for using a strong positive charge , yes you could . It will depend on the molecule and its state ( gas, liquid,solid) and whether it is conducting or semiconducting or an insulator. $\endgroup$
    – anna v
    Sep 13, 2015 at 4:04
  • $\begingroup$ One last question if the energy level of a photon is dependent on the frequency how else could I increase the energy with out changing frequency ? Or do you just increase the numbers of photons $\endgroup$
    – newguy
    Sep 13, 2015 at 4:16
  • $\begingroup$ The energy of a photon is h*nu, cannot change ( well there is the inverse compton effect, but not usable in this sense). The beam has more additive energy but photons cannot sum up in the sense you are thinking. You have to have the appropriate photon source, they have to be generated with the right frequency for the energy level. $\endgroup$
    – anna v
    Sep 13, 2015 at 5:07

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