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

- First principles simulations are performed for an aqueous solution containing a superoxide ion.
- Frequency-structure correlations of water in hydration shell of the superoxide ion are investigated.
- Relaxation of hydrogen bonds, escape dynamics and diffusion of water are looked at.
- Calculations of frequency fluctuations and spectral hole dynamics are performed for water in the hydration shell.
- Links between the vibrational spectral diffusion, hydrogen bonds and other dynamical modes are discussed.

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.