Theoretical strategy to build structural models of microhydrated inorganic systems for the knowledge of their vibrational properties: The case of the hydrated nitrate aerosols
Résumé
This study provides theoretical anharmonic calculations for microhydrated NaNO3-labeled (NaNO3, nH2O)x with a water-to-solute ratio (n) ranging from 1 to 3. A representative geometrical model of these forms was first investigated by simulating the molecular clusters as (NaNO3,1H2O)x with x = 1 to 4. The comparison between the calculated time independent anharmonic frequencies using the B3LYP-D/6-311+G(d,p) method and their experimental counterparts led to the choice of a supercluster model. The most probable structures of (NaNO 3,nH2O)3 molecular system were investigated by using our global search algorithm we developed recently (GSAM code) both at the B3LYP/6-311+G(d,p) and the B3LYP-D/6-311+G(d,p) levels of theory. The quality of the structural model is illustrated by comparing the B3LYP/6-311+G(d,p) and B3LYP-D/6-311+G(d,p) anharmonic vibrational signatures with those obtained from IR experiments. While an average deviation of 16 cm-1 is observed in the case of the B3LYP computations, the deviation is reduced to 7 cm -1 for the B3LYP-D computations. © 2013 American Chemical Society.