Theoretical study of OH-breaking reactions in Na(H2O)n clusters

Highlights: ► Transition-state structures and reaction paths of title reactions were calculated. ► H-loss reactions occur by the capture of the hydrated electron by the H atoms. ► Fragmentation energy of a water molecule was less than the barrier of the H-loss. ► Excess electron – hydrogen interaction was analyzed based on the AIM theory. - Abstract: OH-breaking reactions in Na(H2O)n (n ⩽ 8) clusters were investigated by DFT calculations. The reaction paths were determined by calculating the transition state and the intrinsic reaction coordinate. NaH is formed for n ⩽ 2, while larger clusters undergo H-loss. Though the total hydration energies exceed the barrier of the H-loss, the fragmentation of a single water molecule requires less energy. A protic hydrogen in a water molecule captures the excess electron, and an H atom is released, leaving an OH− in the reactions with n ⩾ 3. The transition state of the H-loss becomes late regarding the OH-breaking, but early with respect to deformation of the clusters with increasing n. On the basis of the Atoms-In-Molecules theory, an interesting bond path was observed between H atoms belonging to different water molecules for n = 6 and 8, which is considered to support the electron-hydrogen interaction