Structure and Properties
The ab initio binding energy between the two water molecules is estimated to be 5-6 kcal/mol, although values between 3 and 8 have been obtained depending on the method. The experimentally measured dissociation energy (including nuclear quantum effects) of (H2O)2 and (D2O)2 are 3.16 ± 0.03 kcal/mol (13.22 ± 0.12 kJ/mol) and 3.56 ± 0.03 kcal/mol (14.88 ± 0.12 kJ/mol), respectively. The values are in excellent agreement with calculations. The O-O distance of the vibrational ground-state is experimentally measured at ca. 2.98 Å; the hydrogen bond is almost linear, but the angle with the plane of the acceptor molecule is about 57°. The vibrational ground-state is known as the linear water dimer (shown in the figure above), which is a near prolate top (viz., in terms of rotational constants, A > B ≈ C). Other configurations of interest include the cyclic dimer and the bifurcated dimer.
Read more about this topic: Water Dimer
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