Hydrogen bonding in methanol studied by infrared spectroscopy

Infrared spectra in the region of the OH stretching band of supercritical methanol (Tc = 239.4 °C, Pc = 8.08 MPa) have been recorded over the 100-400 °C temperature range and 30-100 MPa pressure range. The spectra were obtained using an FT-IR spectrometer equipped with a special high-pressure, high-temperature IR cell and a specially developed measuring technique that utilizes the C-H stretching vibrations as an internal standard. The experimental results show that both pressure and temperature affect the OH stretching band of supercritical methanol. Isobaric heating leads to a strong decrease in the peak intensity and a shift to higher frequencies. Isothermal compression leads to a slight increase in peak intensity and shifts to lower frequencies. These studies are consistent with previous studies conducted at lower pressures and with qualitative models of the extent of hydrogen bonding in liquid and supercritical methanol.