Complexes of atmospheric α-dicarbonyls with water:: FTIR matrix isolation and theoretical study

The complexes of glyoxal (Gly), methylglyoxal (MGly), and diacetyl (DAc) with water have been studied using Fourier transform infrared (FTIR) matrix isolation spectroscopy and MP2 calculations with 6-311++G(2d,2p) basis set. The analysis of the experimental spectra of the Gly(MGly,DAc)/H2O/Ar matrixes indicates formation of one Gly center dot center dot center dot H2O complex, three MGly center dot center dot center dot H2O complexes, and two DAc center dot center dot center dot H2O ones. All the complexes are stabilized by the O-H center dot center dot center dot O(C) hydrogen bond between the water molecule and carbonyl oxygen as evidenced by the strong perturbation of the O-H, CO stretching vibrations. The blue shift of the CH stretching vibration in the Gly center dot center dot center dot H2O complex and in two MGly center dot center dot center dot H2O ones suggests that these complexes are additionally stabilized by the improper C-H center dot center dot center dot O(H-2) hydrogen bonding. The theoretical calculations confirm the experimental findings. They evidence the stability of three hydrogen-bonded Gly center dot center dot center dot H2O and DAc center dot center dot center dot H2O complexes and six MGly center dot center dot center dot H2O ones stabilized by the O-H center dot center dot center dot O(C) hydrogen bond. The calculated vibrational frequencies and geometrical parameters indicate that one DAc center dot center dot H2O complexes, two Gly center dot center dot center dot H2O, and three MGly center dot center dot center dot H2O ones are additionally stabilized by the improper hydrogen bonding between the C-H group and water oxygen. The comparison of the theoretical frequencies with the experimental ones allowed us to attribute the calculated structures to the complexes present in the matrixes.