Hydrogen bonding in liquid methanol at ambient conditions and at high pressure

Neutron and hard X-ray diffraction measurements on liquid methanol at room temperature are presented at pressures ranging from 1 bar to 9 kbar. Under ambient conditions a complete partial structure factor analysis has been performed. The partial structures are not all in agreement with simulation results. Notably, the data show no sign of a sharp feature in the H_O(O/C) partial, implying that the hydrogen between the hydrogen bonded oxygen is less localized than predicted by the standard simulation potentials. The data have been analysed using a continuous random network approach common in the analysis of the structure of tetrahedral network glasses. The pressure-induced change in the scattering intensity is restricted to the momentum transfer range (0 < Q < 2.5 Å^-1), i.e., there is no discernible change in sharp real-space structures. Up to 9 kbar the change in scattering intensity scales to a good approximation with the density.