Ab initio molecular dynamics study of the aqueous HOO(-) ion.

The properties of the hydroperoxide anion, HOO(-), in water play a key role in many biological systems and industrial processes. However the dynamics of HOO(-) and its solvation shell are largely unknown. We have undertaken an ab initio molecular dynamics study of aqueous HOO(-) at ambient temperature in liquid water. Two solvation structures for the hydroperoxide anion account for 90% or more of the configurations in a 25 ps NVT run at 300 K: these have four hydrogen bond donors to the terminal oxygen atom of HOO(-) and either one or two hydrogen bond donors to its middle oxygen atom. The H of HOO(-) is essentially always a donor in an H-bond to a water molecule. Two structures with three donors to the terminal O and either one or two at the middle O are also important. A set of five NVE runs totaling 74 ps found considerable variability in the proportions of time spent in each type of solvation pattern. Mean lifetimes of these patterns ranged from 54 to 109 fs, after which the complexes were observed to transform into different, sometimes less favorable structures. Analysis of the electronic structure associated with different solvation patterns indicates that a traditional Lewis-type picture of hydrogen bonding at the middle oxygen and non-Lewis behavior at the terminal oxygen coexist in aqueous HOO(-). The non-Lewis character of the terminal oxygen is compared to similar observations of the oxygen in the hydrated hydroxide ion from previous ab initio molecular dynamics of OH(-)(aq).