166
4 The Dielectric Properties and Dynamic Structure of Water and Ice
anomalously high mobility of hydronium and hydroxyl ions along with the equal
diffusion coefficients of hydrogen and oxygen atoms; and the picosecond proton
exchange, which coexist along with the many-hour lifetime of water molecules. The
ionic model of water allows one to describe these properties without internal conflicts.
The important innovation of the ionic model is that it accounts for the nuclear
quantum effects and ultrashort picosecond-scale chemical reactions, which were
previously missing in models of the structure of water (see Chap. 1), by introducing
spontaneously formed short-lived ionic pairs with a high concentration n ± =1 mol/l
(2% of the total number of particles, or 1 ion per 50 H 2 O molecules). The average distance between ions is L ≈ 1 nm. This ion–molecular system is highly heterogeneous
and dynamic and contains a wide variety of forms of molecular motion and possible
ways they manifest themselves in the dielectric response. Due to this spatial-time
heterogeneity of water (and ice), their broadband dielectric response is very different
in comparison with those for other dielectrics (see Sect. 3.3).
The ionic model creates the prerequisites for resolving the structural and thermodynamic anomalies of water. In particular, the presence of rapidly fluctuating regions
of high and low density (see Fig. 4.5) paves the way for a quantitative microscopic
description of the anomalously high surface tension, viscosity, and heat capacity of
water, which, however, lie beyond the scope of this book. Accounting for the intermolecular interactions of ionic species can help to explain the anomalous melting,
boiling, and critical points of water. Moreover, as Röntgen assumed long ago [25],
many other anomalous properties of water, such as the non-monotonic behavior of
its density, viscosity, compressibility, specific heat capacity, and the speed of sound
through it, can be explained if water were a two-component mixture. The ionic model
is exactly such a system, where short-lived ionic and molecular species have two
sharply defined interaction potentials, and thus water can be considered as a system
made of two components, or two types of molecular species. Note, however, that apart
from Röntgen’s expectations, the species of water are short-lived (picoseconds for
water and microseconds for ice) thus the difference between them dissolves on large
timescales, as, for example, for the diffusion-averaged D-structure (see Chap. 1). The
averaged ion–ion, ion–molecular, and molecular–molecular interactions are presumably also reduced to the mean interactions, which can be construed as a hydrogen
bonding. Note also that according to the models discussed in this chapter, the latter
concept is inapplicable for the interpretation of the dynamic properties of water on
time intervals shorter than 1 µs, and the ionic model should be used.
References
1. E. Arunan, G.R. Desiraju, R.A. Klein, J. Sadlej, S. Scheiner, I. Alkorta, D.C. Clary, R.H.
Crabtree, J.J. Dannenberg, P. Hobza, H.G. Kjaergaard, A.C. Legon, B. Mennucci, D.J. Nesbitt,
Definition of the hydrogen bond (IUPAC Recommendations 2011). Pure Appl. Chem. 83,
1637–1641 (2011)
2. E.D. Isaacs, A. Shukla, P.M. Platzman, D.R. Hamann, B. Barbielini, C.A. Tulk, Covalency of
the hydrogen bond in Ice: a direct x-ray measurement. Phys. Rev. Lett. 82, 600–603 (1999)
4 The Dielectric Properties and Dynamic Structure of Water and Ice
anomalously high mobility of hydronium and hydroxyl ions along with the equal
diffusion coefficients of hydrogen and oxygen atoms; and the picosecond proton
exchange, which coexist along with the many-hour lifetime of water molecules. The
ionic model of water allows one to describe these properties without internal conflicts.
The important innovation of the ionic model is that it accounts for the nuclear
quantum effects and ultrashort picosecond-scale chemical reactions, which were
previously missing in models of the structure of water (see Chap. 1), by introducing
spontaneously formed short-lived ionic pairs with a high concentration n ± =1 mol/l
(2% of the total number of particles, or 1 ion per 50 H 2 O molecules). The average distance between ions is L ≈ 1 nm. This ion–molecular system is highly heterogeneous
and dynamic and contains a wide variety of forms of molecular motion and possible
ways they manifest themselves in the dielectric response. Due to this spatial-time
heterogeneity of water (and ice), their broadband dielectric response is very different
in comparison with those for other dielectrics (see Sect. 3.3).
The ionic model creates the prerequisites for resolving the structural and thermodynamic anomalies of water. In particular, the presence of rapidly fluctuating regions
of high and low density (see Fig. 4.5) paves the way for a quantitative microscopic
description of the anomalously high surface tension, viscosity, and heat capacity of
water, which, however, lie beyond the scope of this book. Accounting for the intermolecular interactions of ionic species can help to explain the anomalous melting,
boiling, and critical points of water. Moreover, as Röntgen assumed long ago [25],
many other anomalous properties of water, such as the non-monotonic behavior of
its density, viscosity, compressibility, specific heat capacity, and the speed of sound
through it, can be explained if water were a two-component mixture. The ionic model
is exactly such a system, where short-lived ionic and molecular species have two
sharply defined interaction potentials, and thus water can be considered as a system
made of two components, or two types of molecular species. Note, however, that apart
from Röntgen’s expectations, the species of water are short-lived (picoseconds for
water and microseconds for ice) thus the difference between them dissolves on large
timescales, as, for example, for the diffusion-averaged D-structure (see Chap. 1). The
averaged ion–ion, ion–molecular, and molecular–molecular interactions are presumably also reduced to the mean interactions, which can be construed as a hydrogen
bonding. Note also that according to the models discussed in this chapter, the latter
concept is inapplicable for the interpretation of the dynamic properties of water on
time intervals shorter than 1 µs, and the ionic model should be used.
References
1. E. Arunan, G.R. Desiraju, R.A. Klein, J. Sadlej, S. Scheiner, I. Alkorta, D.C. Clary, R.H.
Crabtree, J.J. Dannenberg, P. Hobza, H.G. Kjaergaard, A.C. Legon, B. Mennucci, D.J. Nesbitt,
Definition of the hydrogen bond (IUPAC Recommendations 2011). Pure Appl. Chem. 83,
1637–1641 (2011)
2. E.D. Isaacs, A. Shukla, P.M. Platzman, D.R. Hamann, B. Barbielini, C.A. Tulk, Covalency of
the hydrogen bond in Ice: a direct x-ray measurement. Phys. Rev. Lett. 82, 600–603 (1999)