A Theoretical Perspective on the Actinic Photochemistry of 2-Hydroperoxypropanal

Abstract

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.

Deciphering the Influence of Ground-State Distributions on the Calculation of Photolysis Observables

“…Our group has recently proposed a protocol to determine σ­(λ) using the nuclear ensemble approach (NEA) and ϕ­(λ) by resorting to trajectory surface hopping (TSH) dynamics . This protocol has been applied to VOCs like tert -butyl hydroperoxide, 2-hydroperoxypropanal, or pyruvic acid . TSH simulations and the NEA were also used to successfully unravel the photochemistry of other atmospheric molecules (for examples, see refs − ).…”

Perspective on Theoretical and Experimental Advances in Atmospheric Photochemistry

“…This strategy was used for different atmospheric applications discussed in the CECAM workshop like tert-butyl hydroperoxide (we note that benchmarking TSH with an AIMS run was proposed in this study), 140 methyl hydroxyperoxide, 147 pyruvic acid, 210 CF 3 COCl, 211 HOSO 2 and SO 3 , 199 methyl nitrate, 212 peroxynitrous acid, 213 or 2-hydroxypropanal. 214 The photochemistry of 2-hydroxypropanal highlights the diversity of photochemical processes that multichromophoric VOCs can undergo, ranging from multiple photoproducts, formed either in the excited states or in the ground electronic state with athermal effects, to upfunneling (or diabatic trapping). 215,216 This latter process is illustrated in Figure 6 and is typical of flexible multichromophoric molecules where the molecule remains trapped in a given diabatic state due to a very weak diabatic coupling with other states, slowing down the formation of photoproducts.…”

“…Performing nonadiabatic molecular dynamics for each window and determining their resulting population of photoproducts provide access to photoproduct quantum yields for each energy window, a coarse-grained approximation to the wavelength-dependent quantum yields. This strategy was used for different atmospheric applications discussed in the CECAM workshop like tert -butyl hydroperoxide (we note that benchmarking TSH with an AIMS run was proposed in this study), methyl hydroxyperoxide, pyruvic acid, CF 3 COCl, HOSO 2 and SO 3 , methyl nitrate, peroxynitrous acid, or 2-hydroxypropanal …”

A Theoretical Perspective on the Photochemistry of Boron–Nitrogen Lewis Adducts

“…To achieve these goals, we propose to investigate theoretically these three B–N Lewis adducts by exploiting a combination of quantum-chemical calculations and excited-state (nonadiabatic) molecular dynamics simulations. These computational techniques give access to potential energy curves describing the possible nonradiative pathways, photoabsorption cross-sections, and wavelength-dependent quantum yields (building upon a protocol developed in our group to study atmospheric volatile organic compounds − ). We start this work by detailing the computational methodologies employed for our calculations (Section ), before presenting our main results in Section .…”