Instantaneous normal mode analysis of liquid methanol

The instantaneous normal modes for liquid methanol at 200 K are calculated and related to the topologically linear hydrogen bond network in this syste m. A shoulder observed in the spectra of both collective and single molecul e correlation functions is explained as arising from the presence of "stret ching" modes of the hydrogen bonded network, similarly to what happens in l iquid hydrogen fluoride. In the case of methanol, however, the relation bet ween the chain dynamics and the instantaneous normal modes is much less evi dent, due to the strongest "coupling" of the chain motion to other diffusiv e processes present in the liquid. (C) 2001 American Institute of Physics.