Periodic Reporting for period 4 - SINDAM (Sunlight-Induced Nonadiabatic Dynamics of Atmospheric Molecules)
Berichtszeitraum: 2023-09-01 bis 2024-12-31
The SINDAM project proposes to study the importance of photochemical processes for transient VOCs by developing and using state-of-the-art strategies in computational photochemistry. The principal aims of this project are as follows: (1) establish the importance of photochemical processes in the chemical mechanisms of VOCs, in gas phase and diverse aqueous conditions; (2) determine missing theoretical values for photolysis rate constants and wavelength-dependent quantum yields to create more accurate atmospheric models; (3) develop a widely applicable yet affordable theoretical methodology that accounts for all potential nonradiative mechanisms important for atmospheric; (4) produce an open-access software for atmospheric modelers allowing for the identification of potentially photoreactive VOCs.
We also conducted a series of joint theory/experiment studies on the gas-phase photochemistry of various molecules. For example, we studied the photochemistry of pyruvate and thiophenone by combining computational photochemistry and photoelectron spectroscopy (as well as ultrafast electron diffraction). All these examples showed the maturity of the methods used in computational photochemistry and support their use to predict photolysis quantities for transient VOCs.
Based on its interactions with atmospheric photochemists, the SINDAM team focused on the refinement of strategies for calculating photoabsorption cross-sections. The SINDAM team developed an automated tool, coined AtmoSpec, that uses a user-friendly interface and takes as an input a simple representation of the VOC of interest (SMILES code, xyz geometry) and automates the calculation of photoabsorption cross-sections based on the nuclear ensemble approach. AtmoSpec is open-source and freely available.
The SINDAM team also worked on the development of new strategies to predict the photochemistry of molecular systems. After developing a set of stringent benchmark systems to challenge excited-state dynamics methods, the SINDAM team developed a hierarchy of methods based on the multiple spawning, which offers the quality of an ab initio multiple spawning simulation at nearly the computational cost of surface hopping.
The SINDAM team has been very active in disseminating the results of the action to the computational photochemistry and atmospheric communities. For example, the team worked with atmospheric modelers to test the possibility of developing structure-activity relationships based on the theoretical photoabsorption cross-sections. The team also co-organized a workshop in March 2024 in Lausanne, gathering theoreticians and spectroscopists interested in atmospheric photochemistry and leading to the publication of a perspective article summarizing the main recent developments in the field and future challenges. The SINDAM team also co-led a theoretical challenge for the computational photochemistry community: predicting the photochemistry of a VOC (cyclobutanone) before a time-resolved experiment is performed on the molecule and comparing the prediction with the experimental observables as part of a special issue of the Journal of Chemical Physics. The SINDAM team also disseminated the results of SINDAM to a broader audience via the 'Scientist Next Door' initiative, which uses a web platform and Zoom calls to connect scientists to school-aged children aiming at supporting parents with homeschooling, originally during COVID-19 lockdowns in the UK and extended to support less favored socioeconomic areas.
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.