Intermolecular interaction in formaldehyde dimers

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Abstract
Ab initio SCF calculations with a minimal STO-3G basis set have been performed on dimers of formaldehyde. Two equilibrium dimers have been found on the intermolecular surface. In one of these, dimer stabilization is due to the formation of a hydrogen bond, while in the other, the dipole-dipole interaction is primarily responsible for stabilization. These two equilibrium dimers are comparable in energy and easily interconverted. Upon dimer formation, only a minimal change in electron distribution is observed. Configuration interaction calculations have also been carried out to determine the effect of dimer formation on the n→π* transition energy. These calculations indicate that the n→π* band would be shifted to higher energy by only a few nanometers, relative to the monomer.