THEORETICAL-STUDY OF HYDROGEN-BONDED FORMALDEHYDE WATER COMPLEXES

The system H2CO + H2O has been investigated by means of ab initio SCF and CI calculations. The geometry was SCF-optimized for the complex H2CO + H2O and for one and two additional H2O molecules bound to the optimal H2Co...H2O nuclear arrangements. The binding energy was evaluated with basis set superposition errors and zero-point vibrations taken into account. The solvent shift for the singlet and triplet n-->pi* transitions was determined in CI calculations for the entire system. The solvent shift is found to be strongest (around 1140 cm-1) for the optimally H2O-bonded formaldehyde complexed with one water molecule. The shift is roughly proportional to the number of H2O molecules, going from 0.17 eV (one H2O) to 0. 3 5 eV (two H2O) to 0.47 eV (three H2O) in the singlet (n-->pi*) transition. The influence on the triplet (n-->pi*) transition is wholly parallel.