8
1 A Historical Review of the Structures of Water and Ice
(b)
(c)
(d)
X-rays
Laue
diagram
(a)
Ice
Fig. 1.6 X-ray diffraction experiments with ice crystals. a The experimental schematic. b, c, and
d Laue diagrams of ice crystals for an X-ray beam directed at an angle of 4.6 ◦ C to the c-axis
of the crystal at −5 ◦ C, at −196 ◦ C (liquid nitrogen), and a temperature rising from −180 to −5
◦ C, respectively. Parts (b) to (c) adapted from [23] with permission of the International Union of
Crystallography
theless, X-ray crystallography of ice provided useful information about the relative
position of water molecules, averaged over long periods of time (usually more than
1 s [21]).
Unlike liquid water, ice crystals scatter X-rays non-uniformly, producing areas of
low and high intensity as shown in Fig. 1.6a. Scattering patterns from ice crystals are
known as Laue diagrams,
6 shown in Fig. 1.6b–d. Similar to water, the interpretation
of these patterns requires knowledge about the structure, which for ice reduces to the
knowledge of the crystal lattice structure, which is unknown a priori and cannot be
deduced directly from the geometrical shape of the sample. Everyone knows that the
shapes of snowflakes vary significantly depending on the external conditions, not to
mention the more than 19 forms (both stable and meta-stable ones) of bulk ice that
one can find on the phase diagram of water (see [22]).
In order to describe the structure of ice, Bernal and Fowler relied on the infrared
and Raman spectra, which show common vibrational spectral features for ice, liquid
water, and water vapor (see Fig. 2.13). As the latter was supposed to consist of H 2 O
molecules, the condensed forms of water were assumed to be an assembly of H 2 O
6 Named after Max von Laue, who used diffraction from crystals to prove the short wavelength of
X-rays.
1 A Historical Review of the Structures of Water and Ice
(b)
(c)
(d)
X-rays
Laue
diagram
(a)
Ice
Fig. 1.6 X-ray diffraction experiments with ice crystals. a The experimental schematic. b, c, and
d Laue diagrams of ice crystals for an X-ray beam directed at an angle of 4.6 ◦ C to the c-axis
of the crystal at −5 ◦ C, at −196 ◦ C (liquid nitrogen), and a temperature rising from −180 to −5
◦ C, respectively. Parts (b) to (c) adapted from [23] with permission of the International Union of
Crystallography
theless, X-ray crystallography of ice provided useful information about the relative
position of water molecules, averaged over long periods of time (usually more than
1 s [21]).
Unlike liquid water, ice crystals scatter X-rays non-uniformly, producing areas of
low and high intensity as shown in Fig. 1.6a. Scattering patterns from ice crystals are
known as Laue diagrams,
6 shown in Fig. 1.6b–d. Similar to water, the interpretation
of these patterns requires knowledge about the structure, which for ice reduces to the
knowledge of the crystal lattice structure, which is unknown a priori and cannot be
deduced directly from the geometrical shape of the sample. Everyone knows that the
shapes of snowflakes vary significantly depending on the external conditions, not to
mention the more than 19 forms (both stable and meta-stable ones) of bulk ice that
one can find on the phase diagram of water (see [22]).
In order to describe the structure of ice, Bernal and Fowler relied on the infrared
and Raman spectra, which show common vibrational spectral features for ice, liquid
water, and water vapor (see Fig. 2.13). As the latter was supposed to consist of H 2 O
molecules, the condensed forms of water were assumed to be an assembly of H 2 O
6 Named after Max von Laue, who used diffraction from crystals to prove the short wavelength of
X-rays.