Photodynamics of Gas-Phase Pyruvic Acid Following Light Absorption in the Actinic Region

Abstract

The photochemistry of pyruvic acid has received a large attention due to its relevance to atmospheric chemistry. Pyruvic acid is produced in the troposphere from both biogenic and anthropogenic sources and is a prototypical model for the family of (Formula presented.) -dicarbonyls. What makes the photochemistry of pyruvic acid particularly interesting from a gas-phase perceptive is its expected decarboxylation upon sunlight absorption. The exact photodynamics leading to this release of CO2 remains elusive. In this work, we used a combination of excited- and ground-state ab initio molecular dynamics to unravel the possible mechanisms leading to the decarboxylation of pyruvic acid. Our calculations highlight the importance of a proton-coupled electron transfer mechanism taking place in the first excited electronic state and triggering a nonadiabatic transfer of the molecule to the ground electronic state. The decarboxylation takes place in the ground-electronic state with the concomitant formation of methylhydroxycarbene. We also calculate the photoabsorption cross-section and wavelength-dependent quantum yields for pyruvic acid, highlighting the limits of our theoretical formalism.