Yes, how DOES all that comic book stuff work? An actual, honest-to-goodness PhD has the answers!
So when kinetic energy impacts vibranium, the energy is transformed and released as photons. If this were a science fiction novel, not a superhero movie, there would be some limit to the process, as there are not an infinite amount of photons in an atom. Perhaps the shield would have to be recharged by the sun after seeing use, so it could absorb photons, and if it wasn’t, it would lose the energy transformation power altogether.
On another note, if you give a photon enough energy it becomes a gamma ray, one of the chief forms of ionizing radiation. Could a big enough impact on Cap’s shield cause it to emit gamma radiation?
Could the Hulk do that? If so, could the Hulk smashing Cap’s shield cause enough gamma radiation to transform Cap into a Hulk himself?
See? Now THAT’S science!