Reaction Mechanisms and Dynamics

We have performed successful computational studies for several important organic chemistry reactions, including the Cope rearrangement of 1,5-hexadiene, cycloaddition of cyclopentyne to ethylene, thermal stereomutations of cyclopropane, and isomerization of bicyclo[1.1.0]butane to buta-1,3-diene. We have carried out unprecedented coupled-cluster calculations for CuO₂ and Cu₂O₂ systems, relevant to oxygen activation by metalloenzymes, for photoisomerizations of acetylacetone, for diffusion of atomic oxygen on the silicon surface, for proton-transfer reactions between the dithiophosphinic acids and water molecules relevant to nuclear waste management, for aerobic oxidation of methanol on gold nanoparticles, and for the Co-C bond dissociation in methylcobalamin, relevant to catalytic properties of B₁₂. Our best coupled-cluster methods, combined with the embedding and implicit solvation models and density functional theory, have become very useful in the examination of the strongest-known super photobase synthesized in our department, called FR0-SB, which upon photoexcitation exhibits a change in pK_a so large that the photoexcited FR0-SB* species extracts protons from alcohols. We have also investigated FR0-SB's derivatives and precursors in protic and aprotic solvents. Our methods have proved to be useful in explaining a novel type of singlet-to-singlet thermally activated delayed fluorescence in octatetraene and the formation of CH₃S⁺ ions following the strong-field ionization of CH₃SCN and CH₃NCS. In a more recent and widely publicized work, we have studied the formation of H₃⁺ following the strong-field double ionization of methyl halogens and pseudohalogens. Our state-of-the-art coupled-cluster calculations combined with experiment and ab initio molecular dynamics simulations have allowed us to explain the mechanism, yields, and timescales of H₃⁺ production and develop useful guidelines for examining alternative sources of the trihydrogen cation in the universe. In the past, we also studied the photo-induced charge-transfer ("harpooning") reactions between alkali metal atoms and halides, which were followed by the characterization of quasi-bound states of van der Waals molecules that are precursors of these reactions by combining state-of-the-art ab initio electronic structure and dynamical approaches.