Is this correct?

In a word, no. UV, gamma and x-rays are IONIZING RADIATION this means they have enough energy to remove ELECTRONS and break bonds (which I guess you could say is "smashing" a molecule into constituent atoms). They do not "smash" (I keep using quotes because this is not really a very good way of visualizing what's going on since light has no mass with which to "collide" with anything) apart atomic nuclei, that requires a great deal more energy (like say a neutron at near the speed of light, this is what happens in a nuclear reactor/bomb)

 

UV radiation has enough energy to break up bonds of molecules like certain ones in earths atmosphere, however it does not smash anything like maverick_starstrider has already stated what happens is the particles absorb enough energy from the radiation to leave what ever it is they are bonded to or in the case of ionization they leave what they are orbiting.

 

1) Photons do have momentum and relativistic mass. They can collide and they do.
2) In a nuclear reactor slow neutrons are absorbed

 

1) quantum scattering is incredibly complex and not like a collision at all (of photons or otherwise), try explaining something like compton scattering with a collision visualization

2) Ya, that's true