Ultrafast photochemistry of methyl hydroperoxide on ice particles

Simulations show that photodissociation of methyl hydroperoxide, CH ₃OOH, on water clusters produces a surprisingly wide range of products on a subpicosecond time scale, pointing to the possibility of complex photodegradation pathways for organic peroxides on aerosols and water droplets. Dynamics are computed at several excitation energies at 50 K using a semiempirical PM3 potential surface. CH₃OOH is found to prefer the exterior of the cluster, with the CH₃O group sticking out and the OH group immersed within the cluster. At atmospherically relevant photodissociation wavelengths the OH and CH₃O photofragments remain at the surface of the cluster or embedded within it. However, none of the 25 completed trajectories carried out at the atmospherically relevant photodissociation energies led to recombination of OH and CH₃O to form CH ₃OOH. Within the limited statistics of the available trajectories the predicted yield for the recombination is zero. Instead, various reactions involving the initial fragments and water promptly form a wide range of stable molecular products such as CH₂O, H₂O, H₂, CO, CH₃OH, and H₂O₂.