Theoretical study of binding interactions and vibrational Raman spectra of water in hydrogen-bonded anionic complexes:: (H2O)n- (n=2 and 3), H2O•••X-(X = F, Cl, Br, and I), and H2O•••M- (M = Cu, Ag, and Au)

Binding interactions and Raman spectra of water in hydrogen-bonded anionic complexes have been studied by using the hybrid density functional theory method (B3LYP) and ab initio (MP2) method. In order to explore the influence of hydrogen bond interactions and the anionic effect on the Raman intensities of water, model complexes, such as the negatively charged water clusters ((H2O)(n)(-), n = 2 and 3), the water center dot center dot center dot halide anions (H2O center dot center dot center dot X-, X = F, Cl, Br, and I), and the water-metal atom anionic complexes (H2O center dot center dot center dot M-, M = Cu, Ag, and Au), have been employed in the present calculations. These model complexes contained different types of hydrogen bonds, such as O-H center dot center dot center dot X-, O-H center dot center dot center dot M-, O-H center dot center dot center dot O, and O-H center dot center dot center dot e(-). In particular, the last one is a dipole-bound electron involved in the anionic water clusters. Our results showed that there exists a large enhancement in the off-resonance Raman intensities of both the H-O-H bending mode and the hydrogen-bonded O-H stretching mode, and the enhancement factor is more significant for the former than for the latter. The reasons for these spectral properties can be attributed to the strong polarization effect of the proton acceptors (X-, M-, O, and e(-)) in these hydrogen-bonded complexes. We proposed that the strong Raman signal of the H-O-H bending mode may be used as a fingerprint to address the local microstructures of water molecules in the chemical and biological systems.