[iScience]

not sure if this is the right section to post this in, but in a single atom, when an incident photon has an energy greater than or equal to the binding energy of the particular electron it is incident to, i understand the basic idea/concept on how it is able to be knocked out of the atom.

however, when it comes to a UV photon breaking up a Cl₂ diatom, how exactly is this accomplished? is the UV absorbed by the molecular orbital thereby ejecting that electron and then soon thereafter getting reabsorbed? or.. does the UV give part of the diatom sufficient kinetic energy to break away from the bond energy? this is all just speculation; i find it fun.. but what is the actual mechanism/process?

[Corribus]

I don't know about this specific reaction off the top of my head, but photochemistry in general happens because incoming light photons excite electrons into higher lying electronic states. Such excited states have enough energy to react with a smaller (or no) barrier (thermodynamic activation) or reduces the kinetic barrier in some way (kinetic activation), either by preparing spin states that are conducive to reaction (as in preparation of singlet oxygen) or by preparing selected geometries that are conducive for reaction. Electrons themselves are rarely completely ejected from molecules, as this would usually require higher energy (X-ray) photons.