M:-M0 dM,/dt T due to the excited state ' s dissipation of energy into the " lattice", i.e., other degrees of freedom (molecular vibrations, rotations etc. ) until the BOLTZMANN equilibrium is reached again(Mi) In the BOLtzMann equilibrium, all transverse magnetization must have also disappeared: T2< TI TI=T2 for "small "molecules; however, TI can also be much longer than T2(important for relaxation delay"between scans)! Measuring TI To avoid T2 relaxation, the system must be brought out of BoLTZMANN equilibrium without creating Mxy magnetization: a 180 pulse converts Mz into M-z, then T1 relaxation can occur during a defined period t. For detection of the signal, the remaining Mz/M-z component is turned into the x,y plane by a 90 pulse and the signal intensity measured 180°-τ-90°- acquisition Inversion-recovery experiment From integration of eq, [2-141, one gets zero signal intensity at time to=T, In 2 =0.7TI M2=(1-2exp(t/T)·M M2=99%M t=5T t=3T 0.5 0.0 t/T M2=0 t=T. In2 0.512 dMz / dt = - M M T z - 0 1 [2-14] due to the excited state's dissipation of energy into the "lattice", i.e., other degrees of freedom (molecular vibrations, rotations etc.), until the BOLTZMANN equilibrium is reached again (Mz). In the BOLTZMANN equilibrium, all transverse magnetization must have also disappeared: T2 £ T1 ; T1 = T2 for "small" molecules; however, T1 can also be much longer than T2 (important for "relaxation delay" between scans) ! Measuring T1: To avoid T2 relaxation, the system must be brought out of BOLTZMANN equilibrium without creating Mx,y magnetization: a 180º pulse converts Mz into M-z , then T1 relaxation can occur during a defined period t. For detection of the signal, the remaining Mz / M-z component is turned into the x,y plane by a 90º pulse and the signal intensity measured: 180°-t-90°-acquisition inversion-recovery experiment From integration of eq, [2-14], one gets zero signal intensity at time t0 = T1 ln 2 » 0.7 T1