Reorientation of water molecules free from hydrogen bonding

Abstract

The Mori continued fraction representation of the dipolar memory function K_m(t) has been used to evaluate a spectrum C(ω) involving a single molecular parameter K₀(0), an intermolecular torque dependent parameter K₁(0) and a frequency parameter γ. Knowing these, it is possible to calculate the orientational correlation function C(t) analytically. These parameters have been evaluated by fitting C(ω) to far infrared absorption data for very dilute solutions of water in cyclohexane, carbon tetrachloride and benzene. Therefrom C(t) was found to be non-exponential, with correlation times of ∼0.1 ps, the corresponding loss curves ε″(ω) being asymmetric and peaking at far infrared frequencies. Thus the motion of free, unbonded water molecules cannot be described as rotational diffusion, but rather by a model of large amplitude reorientations, exhibiting distinct solvent dependence.