Ancillary. There are (at least) two ways to break a molecular bond: you can apply enough heat energy to exceed its bond strength, just by blasting it with any energy you have around, which is a process of continually adding more energy and the atoms whanging about until they finally break, or you can use UV tuned to the bond strength, and the bond absorbs a single photon and just pops apart. The latter is interesting because it's cold. All (or most) of the energy of the photon is absorbed by the electrons as the bond breaks. So it doesn't damage surrounding molecules.
This is why UV light damage to cells is interesting. Rather than just nuking the whole cell, like a burn would, a UV photon can just cut a single DNA linkage, leaving the cell alive but broken, and subsequent attempts to replicate can either kill it or make it start misbehaving.