The Electron Distribution and the Location of the Bonded Hydrogen Atom in Crystals

The electron distribution in a bonded hydrogen in crystals is investigated using mainly the VB method with the Gaussian approximation to the Slater wave functions. This approximation appears to be fairly good if the thermal vibration is considerable. In the present paper is studied the C–H bond as an example. It is concluded that the position of the maximum electron density around the proton is located more or less towards the heavier atom, and hence an apparent bond contraction in the X-ray analysis should occur. This seems to be in accord with experimental results. The apparent bond shortening increases and the peak density decreases with increase in the ionic character of the bond. For a constant value of the ionic character, the magnitude of the apparent bond shortening rapidly reaches a certain constant value when thermal vibration becomes large.