Quantum Chemistry Study of Water Ab inito Calculation
F.Benyettou1,2 , S.Hiadsi1 , A.Bendraoua1
1 University of Mohamed Boudiaf, USTO -BP 1505 El Mnaouer -ORAN – Algeria
2.Centre University of Ain Témouchent Road of Sidi Bel Abbes – BP 284, 46000 Ain Témouchent Algeria
Knowledge of structures and energies of the water can provide information on the importance of interactions of several bodies. In a theoretical study, various complexes of water ( – OH, H3O +) with symmetry C1, (OH,– , H3O ,+) (H2O) with symmetry C1, (OH– , H3O +) (H2O) 3 with Cs symmetry; are done by Gaussian software[1], using the Berny algorithm [2] with an approach by ab initio calculations[3], using three methods: Hatree-Fock, MP2 and DFT / B3LYP with the 6-31 + G **. The analysis of results has allowed us: to determine the configurations of the coordinates representing the neutral complex ( – OH,H3O+)(H2O)n. In the comparative study of the distance of a hydrogen bond donor monomer to monomer acceptor in the neutral complex, we find that the distance O …. H successively increases with the number of water molecules added to the neutral complex (OH– ,H3O+)(H2O)n and the energy of its low hydrogen bonding more. The vibrational study of these complexes is in two parts, the first indicates the intra molecular vibrations and intermolecular second vibration. the emergence of three frequency bands (137-630, 1743-1758, 4096-4257) Cm-1 of varying intensities, the first two bands corresponding to intra molecular vibrations, the third band corresponds to the intermolecular vibrations, the frequency bunds ( 4096-4257) Cm-1 meet the OH stretch vibration, the bands (1743-1758) Cm-1 is consistent with the deformation vibration (bending), and the bands (137-630) Cm-1 corresponds to the intra molecular vibrations of the link bridge OH .. O hydrogen.
Experimental values reflect the values of frequencies calculated.
Keywords
Water, Liaison hydrogène, Ab initio, Frequency band.
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