"The internal modes of the water molecule are the symmetric (w1) and asymmetric (w3) stretch of the OH bonds, and the HOH bend (w2). The translational modes of the water-sodium cluster are in analogy with the internal modes: one asymmetric Na-O stretch, one symmetric stretch and one mode which changes the Na-O-Na angle. This third mode does not involve significant movement of the water and, in the case of the whole zeolite, the sodium atoms are bound to the aluminosilicate framework" .