Nuclear Magnetic Resonance in the Cesium Halides

The chemical shifts, the spin-lattice relaxation times, the isotropic exchange coupling ̃ \~A, and the pseudo-dipolar exchange coupling ̃ \~B between cation and anion nuclear spins have been determined in a single crystal of CsBr. The results are: σCs=(-1.9±0.4)×10^-4, σBr=(-2.5±0.3)×10^-4, (T₁)Cs=1050±40 sec, (T₁)Br=0.105±0.020 sec, h^-1| ̃ \~A|=55 sec^-1, h^-1 ̃ \~B=15 or -89 sec^-1. Similar, but less complete, data have been obtained for a single crystal of CsI and a CsCl powder.The results are discussed in terms of existing theories for the chemical shift and exchange interactions in solids. An average of 25% covalent bonding per ion is deduced.The large ratio of T₁ for Cs and Br, respectively, sets an upper limit to the quadrupole moment of Cs¹³³: |Q|<0.004×10^-24 cm². This large difference in the spin-lattice interactions between the nuclear species is responsible for some new effects. The decay time T₂ₑ for the transverse Cs¹³³ magnetization is proportional to H₁²(νCs) for a wide power range of the radio-frequency field at the Cs¹³³ Larmor frequency. It is furthermore possible to build up a transverse Cs¹³³ magnetization by applying, simultaneously with H₁(νCs), a radio-frequency field H₁Br(ν) at a frequency ν=νBr±γCsH₁Cs2π. Here νBr is the bromine precession frequency.A theory of these effects shows that the relatively weak interaction constants ̃ \~A and ̃ \~B between cesium and halogen spins can be determined with much higher accuracy than would have been possible from the usual second moment determinations.