THE OH STRETCHING MODE AND A 3 SPECIES MODEL OF LIQUID METHANOL

An IR cell with variable thickness in the range of 1 mu m is described . It is applied to determine the intensive fundamental OH stretching m ode of liquid methanol and its temperature (T) dependence. Differences between spectra at different T demonstrate one with T increasing and one with T decreasing band. Comparing the decreasing band with measure d spectra of methanol crystals correlates this band with solid-like st rong cooperative OHsc groups. The with T increasing fundamental band i s caused by weak cooperative OHwc groups. These have to be distinguish ed from non H-bonded OH (= OHfree = OHf). This favours the former thre e species model for liquid methanol and water: OHf, OHwc and OHsc. The large half widths (Delta nu(1/2)) of all three OH bands are similar t o Delta nu(1/2) of 1: 1 species with similar strong H-bonds in diluted solutions and indicate three different species with continuous distri butions of distances and orientations. Some authors of a two species m odel - based on fundamental vibrations - observe OHwc and OHsc, but sc arcely OHf. These results clear up apparent discrepancies between spec ies and so-called continuum models of liquids with H-bonds.