2.7 Heavy Water: H/D Isotope Effect
95
Fig. 2.27 The infrared part
of the dynamic conductivity
spectrum of light and heavy
water in: a normal,
b logarithmic and
c double-logarithmic scales.
The vertical dashed line
separates the intramolecular
and intermolecular modes
differences of these spectra for light and heavy water also indicate that there are
nontrivial isotopic effects present.
Maréchal [105], analyzing the structure of the IR spectrum of water, found that
the band ν 2 , which is commonly assigned to molecule bending, has a perfect singleLorentzian shape for light and heavy water. This fact excludes several types of interactions, which was assumed from the analysis of the O–H stretch band ν 1 +ν 3 . Maréchal
concluded that water is made of H 2 O molecules which either perform librations
around one of their three axes (see Fig. 2.26) or perform rotations around an axis
close to their C 2 symmetry axis, b, of a diffusional (relaxational) type. Inasmuch as
molecules are distributed by energy, their rotational energy levels are either below or
above the potential barrier of rotation. The molecules of the first type perform librations around their three axes, while molecules of the second type can rotate around
the b-axis, but keep vibrating along two other axes, a and c. The latter molecules
make water fluid. Such a model satisfactorily explains the properties of the mode ν 2 ,
including its isotopic shift.
95
Fig. 2.27 The infrared part
of the dynamic conductivity
spectrum of light and heavy
water in: a normal,
b logarithmic and
c double-logarithmic scales.
The vertical dashed line
separates the intramolecular
and intermolecular modes
differences of these spectra for light and heavy water also indicate that there are
nontrivial isotopic effects present.
Maréchal [105], analyzing the structure of the IR spectrum of water, found that
the band ν 2 , which is commonly assigned to molecule bending, has a perfect singleLorentzian shape for light and heavy water. This fact excludes several types of interactions, which was assumed from the analysis of the O–H stretch band ν 1 +ν 3 . Maréchal
concluded that water is made of H 2 O molecules which either perform librations
around one of their three axes (see Fig. 2.26) or perform rotations around an axis
close to their C 2 symmetry axis, b, of a diffusional (relaxational) type. Inasmuch as
molecules are distributed by energy, their rotational energy levels are either below or
above the potential barrier of rotation. The molecules of the first type perform librations around their three axes, while molecules of the second type can rotate around
the b-axis, but keep vibrating along two other axes, a and c. The latter molecules
make water fluid. Such a model satisfactorily explains the properties of the mode ν 2 ,
including its isotopic shift.