Raman and DFT study of static, dynamic interactions and isotope effect in pyridazine + H 2O/D 2O systems

Abstract

Polarized Raman and density functional theory (DFT) approach have been applied to study the static and dynamic properties of pyridazine (PRD) in H 2O(W) and D 2O(D) environment. The possible hydrogen bonded (HB) complexes of PRD with H 2O in gas phase and in the water solvation (using IEF-PCM and Onsager models) have been calculated using a B3LYP functional and 6-31+G(d,p)/6-311++G(d,p) basis sets. The static interaction in the PRD + H 2O complex leads to a blue shift in all the Raman modes of PRD and red shift in the O–H modes of water. The IEF-PCM solvation model gives the Raman wavenumbers closest to the experimental values. Raman spectra of ∼962 and 1061 cm −1 mode of PRD in the mixture of PRD + H 2O and PRD + D 2O at different mole fractions of PRD ( x) have been measured. A difference in the wavenumber shift of the two modes of PRD is observed experimentally when PRD is diluted with H 2O and D 2O. The wavenumber shift at maximum dilution ( x = 0.1), however, takes the same value in both H 2O and D 2O. In view of the similar chemical properties of H 2O and D 2O, the difference in the trend of the wavenumber shift is not trivial. It has been explained on the basis of relative values of dipole moments of H 2O, D 2O, and conjugated molecules of PRD with H 2O/D 2O calculated theoretically and the role of larger diffusive property of H 2O compared to D 2O. The dynamical process in the mixture of PRD+ H 2O/D 2O is discussed by studying the variation of the linewidth with concentration. A theoretical model, which is based on the fact that the concentration in microscopic volume fluctuates, fits the experimental results nicely.