Solvent effects on vibrational spectra of hydrogen-bonded complexes of formaldehyde and water: An ab initio study

The vibrational spectrum of the system H2CO + H2O has been predicted by ab initio calculations employing the 6-31G** basis set. The changes in the vibrational characteristics (vibrational frequencies, infrared intensities and Raman activities) from free monomer to a complex have been evaluated. In agreement with experiment, the ab initio calculations show that the stretching C=O and O-H vibrations involved in hydrogen bonding are shifted to lower frequency, corresponding to bond weakening. It was established that for the asymmetric H2CO...H2O structure the ab initio solvent shifts show the best agreement with the experimentally measured shifts.