Very short hydrogen bonds (with O···O separations <2.5Å), in which the position and behaviour of the protons are often ambiguous, have been the subject of many studies by high resolution single crystal neutron diffraction and, more recently, by variable temperature methods. The aim of this proposal is to extend this work to variable temperature and pressure, to gain further knowledge of the HB potential in such cases. We have longstanding interests in the study of hydrogen bonds, particularly with reference to the precise description of hydrogen atom parameters in these. The present proposal is particularly relevant with respect to exploting the potential offered by the SXD instrument with its extended detector array.