Nuclear Quadrupole Coupling Tensors of 2 H in the a-Alum RbAl(SO 4 ) 2 · 12D 2 O and the Dynamical Behaviour of the D 2 O Molecules. An Investigation by NMR and IR

By single crystal NMR the nuclear quadrupole coupling constants eQΦ zz h -1 ( 2 H), the asymmetry parameters η( 2 H) and the direction cosines of the principal axes of the electric field gradient tensors of the 2 H atoms of the two kinds of D 2 O molecules have been determined at 295 K in RbAl(SO 4 ) 2 · 12D 2 O. The results show that the D 2 O molecules surrounding the ion Al 3+ are “static” within the time scale of the 2 H nuclear quadrupole interaction while the D 2 O belonging to the octahedron around the Rb + undergoes fast reorientations around the twofold molecular axis. For the two kinds of D 2 O in the alum we found: eQΦ zz (1) h -1 ( 2 H) = 186.5 kHz, η (1) ,( 2 H) = 0.1234; eQΦ zz (2) h -1 (2H) = 169.7 kHz,η (2) ( 2 H) = 0.1297; eQΦ zz (3) h -1 ( 2 H) = 122.1 kHz, ( 2 H) = 0.8087. eQΦ zz (1) and eQΦ zz (2) belong to the "static" D 2 O molecules and an assignment to the two different 2 H atoms has been performed. The IR spectra of RbAl(SO 4 ) 2 · 12(H 1-x D x ) 2 O have been investigated, and for the O - D stretching frequencies values of 2145 cm -1 , 2235 cm -1 , 2470 cm -1 and 2525 cm -1 have been obtained. They agree well with the relations between ṽ OD and eQΦ zz h -1 ( 2 H) given in the literature.