Triplet State Radical Chemistry: Significance of the Reaction of SO with HCOOH and HNO.

The triplet excited states of sulfur dioxide can be accessed in the UV region and have a lifetime large enough that they can react with atmospheric trace gases. In this work, we report high level ab initio calculations for the reaction of the aB and bA excited states of SO with weak and strong acidic species such as HCOOH and HNO, aimed to extend the chemistry reported in previous studies with nonacidic H atoms (water and alkanes). The reactions investigated in this work are very versatile and follow different kinds of mechanisms, namely, proton-coupled electron transfer () and conventional hydrogen atom transfer () mechanisms.

Controlling the Diradical Character of Thiele Like Compounds.

Organic diradicals play an important role in many fields of chemistry, biochemistry, and materials science. In this work, by means of high-level theoretical calculations, we have investigated the effect of representative chemical substituents in -quinodimethane (QDM) and Thiele's hydrocarbons with respect to the singlet-triplet energy gap, a feature characterizing their diradical character. We show how the nature of the substituents has a very important effect in controlling the singlet-triplet energy gap so that several compounds show diradical features in their ground electronic state.

Fast Sulfate Formation Initiated by the Spin-Forbidden Excitation of SO at the Air-Water Interface.

The multiphase oxidation of SO to sulfate in aerosol particles is a key process in atmospheric chemistry. However, there is a large gap between the observed and simulated sulfate concentrations during severe haze events. To fill in the gaps in understanding SO oxidation chemistry, a combination of experiments and theoretical calculations provided evidence for the direct, spin-forbidden excitation of SO to its triplet states using UVA photons at an air-water interface, followed by reactions with water and O that facilitate the rapid formation of sulfate.

Photosensitization mechanisms at the air-water interface of aqueous aerosols.

Photosensitization reactions are believed to provide a key contribution to the overall oxidation chemistry of the Earth's atmosphere. Generally, these processes take place on the surface of aqueous aerosols, where organic surfactants accumulate and react, either directly or indirectly, with the activated photosensitizer. However, the mechanisms involved in these important interfacial phenomena are still poorly known.