The primary photolysis of aqueous acrylate

Abstract

We apply transient absorption spectroscopy supported by 2D-IR spectroscopy and density functional theory calculations to determine the primary photolysis of acrylate excited via the transition at 200 nm. Upon photoexcitation, about half of the excited acrylate anions return to the ground state and relax to equilibrium in 5 ps primarily through intermolecular coupling between the carboxylate group and the surrounding water. The rest of the excited acrylate anions dissociate. Three dissociation channels have been identified. In one reaction, decarboxylation of acrylate forms CO₂ and CH₂CH⁻. CH₂CH⁻ is protonated by water and forms ethene, C₂H₄, in <0.8 ps. In the second reaction, the excited acrylate anions dissociate to H₂CCHO⁻ and CO. In about 20 ps, H₂CCHO⁻ picks up a proton from water to produce vinyl alcohol, H₂CCHOH. A third dissociation channel forms H₂CCHO˙ and CO⁻. H₂CCHO˙ abstracts a hydrogen atom from water and forms vinyl alcohol. Vinyl alcohol will tautomerize to acetaldehyde, but this occurs on a time scale longer than the experimental observation time of 0.56 ns.