UV-induced photoreaction pathways of salicylic acid: Identification of the fourth stable conformer and ketoketene–water complex

Photoreaction pathways of salicylic acid have been investigated by the low-temperature matrix-isolation infrared spectroscopy with an aid of the density-functional-theory calculations. Only the most stable E form existed in an argon matrix. The second stable R form and the fourth stable H form were produced by UV irradiation (λ > 290 nm). The third stable O form was assumed to return immediately to E form even if it was produced. Ketoketene–water complex was yielded from R form by dissociation of the H and OH parts interacting through intramolecular hydrogen bonding upon prolonged UV irradiation.