Rayleigh light scattering of hydrogen bonded clusters investigated by means of ab initio calculations

Ab initio calculations of depolarization ratios and intensities of classically scattered light, in terms of dipole polarizabilities and polarizability anisotropies, are reported for different hydrogen bonded molecular clusters. Five different groups of organic heterodimers formed with water are considered: HCHO...H2O, CH3HO...H2O, HCOOH...H2O, CH3CN...H2O, and (CH3)(2)CO...H2O, together with the water dimer H2O...H2O. The geometries of all complexes have been optimized by means of the second-order Moller-Plesset many-body perturbation theory (MP2), using the augmented correlation-consistent basis set with polarized valence of double-zeta quality (aug-cc-pVDZ). The calculated average dipole polarizabilities of the isolated molecules are in good agreement with available experimental results. The calculations are then extended to the complexes and, from these, the Rayleigh scattering activities and depolarization ratio changes, upon hydrogen bond formation, are obtained and analysed. The differences in activity and depolarization for Rayleigh scattered radiation between two groups of isomers, (i) HCN...H2O and H2O...HCN and (ii) CH3HO...H2O and CH3OH...OH2, have also been investigated.