Mechanistic Insights into UV Spectral Changes of Pyruvic Acid and Pyruvate Part 2: Interaction with a Water Cluster

Abstract

We investigate the unique photochemistry and photophysics occurring at air–water interfaces by studying how the UV spectra of pyruvic acid (PA) and pyruvate are impacted by interactions with water clusters. The excitation energy calculated at the ωB97X-D/aug-cc-pVTZ level of theory for the trans-pyruvic acid conformer redshifts from 348.8 nm in vacuo to 351.6 nm on the surface of a water cluster; in contrast its excitation energy in water is 340.0 nm. These effects are interpreted in the context of interactions with the n → π* transition. We observe that explicit solvent interactions and the bulk properties of the solvent lead to the experimentally observed blueshift of pyruvic acid upon solvatization in water, a blueshift in the region of the spectrum where solar intensity is changing by several orders of magnitude within the range of tens of nm. Thus, perturbations commonly found in the vicinity of aerosol surfaces will critically affect the lifetime of this key atmospheric intermediate.