UV Photochemistry of Acetylacetaldehyde Trapped in Cryogenic Matrices

The broad band UV photochemistry of acetoacetaldehyde, the hydrid form between malonaldehyde and acetylacetone (the two other most simple molecules exhibiting an intramolecular proton transfer), trapped in four cryogenic matrices, neon, nitrogen, argon and xenon, has been studied by IRTF spectroscopy. These experimental re- sults have been supported by B3LYP/6-311G++(2d,2p) calculations in order to get S0 minima together with their harmonic frequencies. On those minima we have also calcu- lated their vibrationnally-resolved UV absorption spectra at the time-dependent DFT !B97XD/ 6-311++G(2d,2p) level. After deposition, only the two chelated forms are observed while they isomerize upon UV irradiation toward nonchelated species. From UV irradiation eects we have identied several nonchelated isomers, capable, in turn, of isomerizing and fragmenting, even if this last phenomenon seems to be most unlikely due to cryogenic cages connment. Based on these ndings, we have attempted a rst approach to the reactionary path of electronic relaxation. It appeared that, as with acetylacetone, the path of electronic relaxation seems to involve triplet states.