A Theoretical Perspective on the Actinic Photochemistry of 2‑Hydroperoxypropanal

The photochemical reactions triggered by the sunlight
absorption
of transient volatile organic compounds in the troposphere are notoriously
difficult to characterize experimentally due to the unstable and short-lived
nature of these organic molecules. Some members of this family of
compounds are likely to exhibit a rich photochemistry given the diversity
of functional groups they can bear. Even more interesting is the photochemical
fate of volatile organic compounds bearing more than one functional
group that can absorb lightthis is the case, for example,
of α-hydroperoxycarbonyls, which are formed during the oxidation
of isoprene. Experimental observables characterizing the photochemistry
of these molecules like photoabsorption cross-sections or photolysis
quantum yields are currently missing, and we propose here to leverage
a recently developed computational protocol to predict in silico the
photochemical fate of 2-hydroperoxypropanal (2-HPP) in the actinic
region. We combine different levels of electronic structure methodsSCS-ADC(2)
and XMS-CASPT2with the nuclear ensemble approach and trajectory
surface hopping to understand the mechanistic details of the possible
nonradiative processes of 2-HPP. In particular, we predict the photoabsorption
cross-section and the wavelength-dependent quantum yields for the
observed photolytic pathways and combine them to determine in silico
photolysis rate constants. The limitations of our protocol and possible
future improvements are discussed.