Mobility of water in Linde type A synthetic zeolites: an inelastic neutron scattering study

In the present work the effects produced by cation substitution on the dynamics of water in Linde typeA (LTA) synthetic zeoliteswere investigated bymeans of inelastic neutron spectroscopy (INS). Inparticular,we performedmeasurements on fully hydrated Na-A and Mg-exchanged-A zeolites. The collected INS spectra showed two broad bands due to the vibrational (water–cation and hydrogen bond stretch) and librational (rock, twist and wag) modes of water. To quantitatively assign these various modes, the spectra were decomposed into Gaussian components and compared with the INS spectra of ice and of water in other zeolites. The observed shifts of the band positions for different temperatures were discussed. In particular, a slight shift of the three librational modes towards higher frequencies with increasing temperature was revealed for both samples. The hydrogen bond stretching and librationalmodes of water in Na-A and Mg50-A zeolites shift to lower frequencies with respect to ice. Furthermore, in the case of Mg50-A zeolite, we observed a shift upwards in frequencyof librational bands with respect toNa-Azeolite. The obtained results were discussed in relation to our previous elastic and quasi-elastic neutron scattering (ENS and QENS respectively) measurements on the same samples.