Theoretical Study of the Structure, Energetics, and the n−π* Electronic Transition of the Acetone + nH2O (n = 1−3) Complexes

The structure, energetics, and vibrational spectra of the (CH3)2CO·(H2O)n (n = 1−3) complexes have been studied using density functional and ab initio B3LYP, MP2, and CCSD(T) methods. The excitation energies and the oscillator strength for the n−π* electronic transition in acetone and acetone−water complexes have been calculated using the CIS, CASSCF, and CASPT2 approaches. The results show that the first water molecule is coordinated to the carbonyl group of acetone, while the oxygen atom of H2O forms a weak hydrogen bond with a methyl hydrogen. The second H2O occupies a position between the first water and a methyl group, and the third H2O occupies a position between the second H2O and the methyl hydrogen of acetone. The energies of the coordination of the first, second, and third water molecules to the complexes are 3.7, 5.7, and 6.7 kcal/mol, respectively. The formation of the (CH3)2CO·(H2O)n complexes results in the shift of vibrational frequencies for acetone and water, particularly, red shifts for ...