When scientists analyze proteins (chains of amino acids), often times light spectroscopy is used. Light is passes through a cuvet containing dissolved protein, and the absorption is measured. My question is: How do bonds absorb energy? What is the actual mechanism? I have been told that the wavelength of the bond must match that of the radiation being absorbed, but I do not understand this explanation. If the wavelengths match, would we note expect amplification of the bond (constructive interference)? And what does it mean to speak of bonds as "wavelengths"? Is that simply another way of referring to the length of the bond?