The SINDAM project led to the development of a protocol for the calculation of photolysis rate constant and a new series of methods for excited-state dynamics that offer a compromise between ab initio multiple spawning and trajectory surface hopping. Our research group successfully applied the protocol for photolysis quantities to study and characterize the gas-phase photochemistry of the molecules 2-HPP, pyruvic acid, pyruvate, thiophenone, cyclobutanone, CF3COCl, o-nitrophenol, and B-N compounds. Other computational photochemistry groups have already adopted our protocol to determine photolysis rate constants of small organic and inorganic molecules. We also worked alongside spectroscopists to validate the photochemical pathways determined theoretically and identify specific unexpected photoproducts. For example, our theoretical work combined with photoelectron spectroscopy revealed that, upon irradiation in the UVA region, gas-phase pyruvate photodecomposes to form a CO2, CO, and an unexpected methide anion. Combining our theoretical work with time-resolved ultrafast electron diffraction, we could unravel the early-time formation of photoproducts upon irradiation of thiophenone.
Another key development of the SINDAM project is the theoretical determination of photoabsorption cross-sections for VOCs. This quantity enters the photolysis rate constant equation and provides a first key indication on the timescale of photolysis for a given VOC. Our group develops a protocol based on accurate sampling for the determination of photoabsorption cross-section for flexible molecules like VOCs. In addition, we released an open-source and freely available software, AtmoSpec, that automates the process of calculating photoabsorption cross-sections for VOCs. AtmoSpec does not require the user to be an expert in computational chemistry and can be used to streamline the decision process of including or not the photolysis of transient VOCs in chemical mechanisms.
