The proton relaxation of CH3OD in the presence of Co(II) ions, as studied by spin-echo techniques

By measurement of the proton relaxation times T 1 and T 2 of CH3OD containing Co++ ions in dilute solution and the dependence of the observed decay time (T 2 †) on t ep the separation between pulses in a Carr-Purcell sequence the coordination number is shown to be six. Since this result has previously been obtained by an independent method, the use of the dependence of T 2 † on t ep to determine coordination numbers is justified for solutions of paramagnetic ions. The validity of analytical expressions derived previously has been checked by numerical methods, and the analytical expression is shown to be valid even in the presence of H 0 and H 1 inhomogeneity and inaccurate pulses of finite duration, provided that the Meiboom-Gill method is used. In an Appendix insight derived from the results of the numerical solutions is used to give a brief derivation of the dependence of T 2 † on H 0, exchange rate and t ep.