Dimers of ethanol

The energy difference between the gauche and trans structures of ethanol is determined at the CCSD(T)/ aug-cc-pVTZ level. Five classes of dimer structures exist due to the two monomer conformations. In a systematic way 600 structures were generated as initial structures for the dimer geometry optimization. On the MP2/6-311++(3df,2p) level the following minima on the potential energy surface were found: 10 conformations with oxygen as the proton donor and 14 conformations with only carbon as the proton donor. Saddle points and barrier heights of five rearrangement reactions were calculated on the MP2/6-31++G-(2d,p) level. The consequences of these rearangement reactions are: only six conformations of the ethanol dimers exist with oxygen as the proton donor and at low temperatures some conformations with only carbon atoms as the proton donor may be stable. A qualitative agreement exists between the experimental OH stretching spectrum and the corresponding calculated spectrum by use of the double harmonic approximation.