An ab initio molecular dynamics study of the hydrogen bonded structure, dynamics and vibrational spectral diffusion of water in the ion hydration shell of a superoxide ion

Abstract

We present a first principles simulation study of vibrational spectral diffusion and hydrogen bond dynamics in aqueous solution of a superoxide ion. It is found that the OD modes in the hydration shell have different stretching frequencies than the bulk water. The dynamical aspects of vibrational spectral diffusion of hydration shell water molecules reveal three time scales: A short-time relaxation (∼100 fs) corresponding to the dynamics of intact ion–water hydrogen bonds, a slower relaxation (∼4.2 ps) corresponding to the lifetimes of ion–water hydrogen bonds and a third longer time scale (∼30 ps) corresponding to the escape dynamics of water from the anion hydration shell. However, when the vibrational spectral diffusion is calculated over all the OD modes, only two time scales of ∼200 fs and ∼2.4 ps are found without the slowest component of ∼30 ps.