Longitudinal relaxation time, hydrogens

For the aliphatic alcohols methanol, ethanol, and propanol, three relaxation times were observed. Then there is the question of which relaxation process most determines Vp (see. Eq. (36)). In the analysis of the rate constant dependence on the longitudinal relaxation time, the longest time, Ti, corresponding to hydrogen bond rupture in clusters caused by hydrogen bond formation was used earlier. 

Laser heating of the sample combined with MAS yields an enhanced resolution of the H NMR spectra of molecules adsorbed in zeolites. The fast increase of the temperature fi om a value at which the reaction is too slow to be measured to the reaction temperature allows the determination of reaction rates and hydrogen transfer rates in order of magnitude of more than one per minute. The time evolution of the system can be monitored by H NMR in steps, which are limited by the longitudinal relaxation time. 

For hydrides with very weak or not observable Vmh bands especially important becomes the use of NMR techniques. The main H NMR evidence of dihydrogen bonding are the up-held shift of the hydride resonance by 0.1-0.8 ppm and the decrease of its longitudinal relaxation time (T ) 1.5-3 times (Table 6). When the hydride ligand is not involved in the hydrogen bond, its resonance shifts to lower held. ... 

Figure 2 The density dependence of the proton T, of ammonia gas at 300 K. The density of an ideal gas at STP is defined as 1 amagat. The solid line is the best fit of a theoretical model that allowed for multiple relaxation times to the data. Reproduced with permission of the American Physical Society from Lemaire C and Armstrong RL (1984) Proton spin longitudinal relaxation time in gaseous ammonia and hydrogen chloride. Journal of Chemical Physics 1626-1631.

The IR or SR pulse sequences give access to the longitudinal (or spin-lattice) relaxation time Tj of the different hydrogen components within... 

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