DENSITY AND TEMPERATURE EFFECTS ON THE HYDROGEN-BOND STRUCTURE OF LIQUID METHANOL

The hydrogen bond structure of liquid methanol was investigated as a f unction of pressure and temperature up to 2.8 kbar and from 297 to 413 K. Chemical. shifts of the CH3 and OH groups were monitored throughou t this pressure and temperature regime, and the chemical shift differe nce between these two groups was used to describe changes of the hydro gen bond network in methanol. The hydrogen bond equilibrium was invest igated using molecular dynamics simulations and a phenomenological mod el describing clustering in liquid methanol. Results are presented con cerning the size and distribution of hydrogen-bonded clusters in metha nol as a function of pressure and temperature. The results indicate th at the extent of hydrogen bonding decreases upon an increase in temper ature. The results for pressure are equivocal, the phenomenological mo del suggests that hydrogen bonding decreases with increasing pressure, which supports earlier interpretations regarding the measured self-di ffusion coefficients in deuterated methanol as a function of pressure. The molecular dynamics simulations, however, show an increase in hydr ogen bonding with increasing pressure.