Vibrational frequencies of molecules, infrared light, adsorption and emission of light, bingo bango bongo
It honestly doesn't matter if I understand it (even though I've been studying it for years) because you literally just argued that it doesn't count because you don't understand it. It's the single dumbest thing I've ever seen you say, and I make a habit of reading your posts because you're the single dumbest poster I've ever seen.