Photodissociation of protonated formic acid Jayshree Nagesh, Shivangi Nangia, Marissa Saunders, Diane Neff & Lori Burns Telluride School of Theoretical Chemistry July 25, Lizard Head Group

Protonated Formic Acid is Model System for Ester Decomposition Ester Hydrolysis Atmospheric Pollutant Elucidate formation of organic and biological molecules Astrochemistry

Background 70 % 42 ±3 kcal/mol 30 % 18±4 kcal/mol Mackey, G.I. et al. JACS, 100:24 (1978)‏ What factors favor the formation of the less thermodynamically stable product??? Protonated formic acid

More Background Sekiguchi et al., J Am Soc Mass Spectrom 2004, 15,

Research Questions Is the photochemical dissociation of formic acid similar to the thermally driven dissociation? How important is the quantum nature of proton migration in the dissociation pathway? How can we characterize energy transfer through the molecule? – Beyond the Born-Oppenheimer approximation!

Photodissociation Pathways in Excited States Dissociation occurs along C–O bond coordinate Consider species trapped by jet cooling into HCO–OH 2 + form Photoexcitation (~230 nm) induces transition to A 1 A manifold Anticipated radiative lifetime ~40 ns Evolution among several excited states leads to dissociation along alternate pathways Sekiguchi et al., J Am Soc Mass Spectrom 2004, 15,

Quantum nature of proton Sekiguchi et al. used “on the fly” direct dynamics which uses classical equations of motion Proton transfer is better described by quantum dynamics Nuclear-electronic orbital (NEO) method (Hammes-Schiffer)‏ – Potential energy surface as a function of electron and proton Webb et al J Chem Phys , Sekiguchi et al., J Am Soc Mass Spectrom 2004, 15,

Energy Transfer Through the Molecule John Tully's TSTC presentation Exothermic protonation drives the endothermic dissociation in the thermally activated process Incorporating excited states allows for the investigation of multiple dissociation pathways – Surface Hopping

The Big Picture!! Formic acid serves as a model system for understanding acid catalyzed ester hydrolysis Photodissociation studies provide insight into microscopic mechanism of reactions

Acknowledgements Telluride School of Theoretical Studies Prof. Jack Simons Prof. John Tully Prof. Rigoberto Hernandez Prof. Geoff Hutchinson Nana Naisbitt & TSRC Staff