Molecular Dynamics of Photoinduced Reactions of Acrylic Acid: Products, Mechanisms, and Comparison with Experiment.

The photochemistry of acrylic acid is of considerable atmospheric importance. However, the mechanisms and the time scales of the reactions involved are unknown. In this work, the products, yields, and reaction pathways of acrylic acid photochemistry are investigated theoretically by molecular dynamics simulations on the ππ* excited state. Two methods were used to describe the excited state: the semiempirical OM2/MRCI and the ab initio ADC(2). Over 100 trajectories were computed with each method. A rich variety of reaction channels including mechanisms, time scales, and yields are predicted for the single potential energy surface used. Main findings include: (1) Products predicted by the calculations are in good agreement with experiments; (2) ADC(2) seems to validate OM2/MRCI predictions on main aspects of mechanisms, but not on time scales. It is concluded that both semiempirical and ab initio molecular dynamics simulations have useful advantages for the description of photochemical dynamics of carboxylic acids.