We investigate the potential energy surface (PES) and the unimolecular dissociation pathways for molecular systems of atmospheric and industrial importance.

For example, we explored the unimolecular decomposition of bromoacetaldehyde (BrCH₂CHO) – a significant stable brominated organic intermediate in the bromine-ethylene addition reaction during arctic bromine explosion events. We performed high-level quantum chemical calculations, and Rice−Ramsperger−Kassel−Marcus (RRKM)/Master equation analysis under photolytic and thermal conditions. We found that there are 14 possible decomposition channels for BrCH₂CHO on a PES with eight wells. Assuming a singlet ground-state potential energy surface dominated photodynamics, we studied primary photodissociation yields of BrCH₂CHO under various collision energy transfer conditions. At ground level, under tropospheric actinic flux and atmospheric pressure, depending on collisional energy transfer (150 cm⁻¹ < ⟨ΔE_down⟩ < 450 cm⁻¹), 33−78% of BrCH₂CHO directly photodissociates at 320 nm. This is notably higher than acetaldehyde (14%) due to favorable Br and HBr-forming dissociation channels. Photodissociation product branching fractions are relatively independent of collisional energy transfer. At ⟨ΔEdown⟩ = 300 cm⁻¹ and 320 nm excitation, 27% involves C−C bond fission, 11% C−Br bond fission, 7% HBr elimination, and < 2% each for consecutive O−Br fission and brominated vinyl alcohol photo-tautomerization, notably different from acetaldehyde’s photodissociation.