Diffusional and vibrational dynamics of water in NaA zeolites by neutron and Fourier transform infrared spectroscopy

This paper reports themost recent results of a detailed spectroscopic analysis of water confined in NaA zeolitic matrix, performed, as a function of temperature and hydration level, by means of the simultaneous use of incoherent quasielastic neutron scattering (IQENS) and Fourier transform infrared (FT-IR) absorption. The diffusive process reveals a rather wide distribution of relaxation times. Furthermore, we observed a Q-dependence of the mean relaxation time <τ> which does not disagree with the mode coupling theory for associated liquids. As far as vibrational dynamics is concerned, the spectral substructure of the H2O bending (1500–1800 cm−1) and O–H stretching (3000–3800 cm−1) bands has been interpreted in the framework of actual theories for associated liquids and on the basis of previous measurements performed, by Raman scattering, on water confined in a controlled silica glass (GelSil). From a comparison of the results in these two cases, the ‘structure-maker’ role on confined water, played by the NaA zeolite, and the ‘structure-breaker’ role, played by the GelSil, have been clearly shown.