Hydrogen bonding under pressure

The motivation of this paper is to examine how hydrogen bonds are affected by pressure. We find that, in cooperative hydrogen bonds, the distances between neighbouring hydrogen atoms decrease up to similar to 2 Angstrom under pressure, and then, the parent structure breaks down. It is well known that, at 0.1 MPa, the hydrogen bonds, X-H - - - Y can be described by potential functions involving these three atoms only. However, under pressure, because other neighbouring atoms of hydrogen bonds in a given structure come closer to it, these may require modifications. We describe one such modification in the Lippincott & Schroeder type potential function by including the terms corresponding to these additional non-bended interactions. Calculations for O-H distances show that, differences between this and the isolated case are, on an average, 0.0005 Angstrom. This is much smaller that the present precision (similar to 0.003 Angstrom) of neutron diffraction experiments. Similarly the recent data on O-H stretch frequency versus O - - - O distance are also reproduced by the isolated case. This allows us to conclude that various correlations (r versus R, v versus R) derived at 0.1 MPa, continue to hold for high pressure situations.