Formation of Hydrogen Peroxide from O(HO) Clusters.

Hydrogen peroxide (HO) has recently received much attention as a safe and clean energy carrier for hydrogen molecules. In this study, based on direct ab initio molecular dynamics (AIMD) calculations, we demonstrated that HO is directly formed via the photoelectron detachment of O(HO) ( = 1-6) (water clusters of an oxygen radical anion). Three electronic states of oxygen atoms were examined in the calculations: O(X)(HO) (X = P, D, and S states). After the photoelectron detachment of O(HO) ( = 1) to the S state, a complex comprising O(S) and HO, O()-OH, was formed. A hydrogen atom of HO immediately transferred to O(S) during an intracluster reaction to form HO as the final product. Simulations were run to obtain a total of 33 trajectories for = 1 that all led to the formation of HO. The average reaction time of HO formation was calculated to be 57.7 fs in the case of = 1, indicating that the reaction was completed within 100 fs of electron detachment. All the reaction systems O(S)(HO) ( = 1-6) indicated the formation of HO by the same mechanism. The reaction times for = 2-6 were calculated to range between 80 and 180 fs, indicating that the reaction for = 1 is faster than that of the larger clusters, that is, the larger the cluster size, the slower the reaction is. The reaction dynamics of the triplet O(P) and singlet O(D) potential energy surfaces were calculated for comparison. All calculations yielded the dissociation product O(X)(HO) → O(X) + (HO) (X = P and D), indicating that the O(S) state contributes to the formation of HO. The reaction mechanism was discussed based on the theoretical results.