atomic physics - Can a photon be absorbed by a proton?

When incident light passes through a hydrogen gas, for example, does it have 50% chance (since it's a 1:1 ratio of protons to electrons) of getting absorbed by the proton? Any chance at all? If no, why not? Does a proton have a "bandgap"? If yes, what happens when a photon is absorbed by a proton?

Answer

Does a proton have a "bandgap"? If yes, what happens when a photon is absorbed by a proton?

For single protons, as in a plasma , there exists Compton scattering .

The photon transfers part of its energy to the proton and scatters off at a lower energy/frequency, the proton taking up the energy-momentum balance. This is a continuous spectrum, from very low energies on.

For high energy photons the quark structure of the proton can be probed and depending on the energy more particles are created by the interaction with the constituent quarks. There are no energy levels for the quarks within the proton.

There do exist baryonic resonances, i.e. with the same three quarks at higher excited states. If one were to scatter gammas of the appropriate energy, some resonances will be excited , for example the N(1520) decays into a proton and a gamma so in the crossection a resonance will be seen passing that energy of center of mass in proton gamma scattering.

This is a theoretical study of gamma proton scattering at high energies.