Aqueous Id has explained what Hydrogen Bonds are. In the case of water their enthalpy of formation is about 20kJ/mole. By comparison the covalent O-H bond in water has an enthalpy ~ 450kJ/mol, so around 20 times stronger. More generally, light in the UV, visible and occasionally IR regions can be strong enough to break chemical bonds, which is the basis of photochemistry: https://en.wikipedia.org/wiki/Photochemistry Usually this involves the formation of free radicals rather than than ions. The energy needed to break bonds is generally quite a bit less than that needed to detach a free electron, because in photochemical bond-breaking all the electrons end up in bound states. But indeed microwaves do not have the energy to do this. Actually it is interesting that the Hydrogen Bond is what gives water its anomalously high specific heat capacity: the H bonds provide another series of energy levels to populate, in addition to the higher rotational and internal vibrational energy levels.