Molecular hydrogen diffraction intensity

PI Z = 1 Dn = 1.475 R = 0.05 for 961 neutron intensities. This is a neutron-diffraction refinement of a structure previously determined by X-ray diffraction.56 All of the hydroxyl groups are involved in inter-molecular hydrogen-bonds which form infinite chains, with H O distances ranging from 175.5 to 200.2 pm, and O-H O angles... 

Deformation density maps have been used to examine the effects of hydrogen bonding on the electron distribution in molecules. In this method, the deformation density (or electrostatic potential) measured experimentally for the hydrogen-bonded molecule in the crystal is compared with that calculated theoretically for the isolated molecule. Since both the experiment and theory are concerned with small differences between large quantities, very high precision is necessary in both. In the case of the experiment, this requires very accurate diffraction intensity measurements at low temperature with good thermal motion corrections. In the case of theory, it requires a high level of ab-initio molecular orbital approximation, as discussed in Chapter 4. 

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