On the Theoretical Determination of Photolysis Properties for Atmospheric Volatile Organic Compounds

Volatile
organic compounds (VOCs) are ubiquitous atmospheric molecules
that generate a complex network of chemical reactions in the troposphere,
often triggered by the absorption of sunlight. Understanding the VOC
composition of the atmosphere relies on our ability to characterize all of their
possible reaction pathways. When considering reactions of (transient)
VOCs with sunlight, the availability of photolysis rate constants,
utilized in general atmospheric models, is often out of experimental
reach due to the unstable nature of these molecules. Here, we show
how recent advances in computational photochemistry allow us to calculate in silico the different ingredients of a photolysis rate
constant, namely, the photoabsorption cross-section and wavelength-dependent
quantum yields. The rich photochemistry of tert-butyl
hydroperoxide, for which experimental data are available, is employed
to test our protocol and highlight the strengths and weaknesses of
different levels of electronic structure and nonadiabatic molecular
dynamics to study the photochemistry of (transient) VOCs.