Spin latice relaxation time

The spin-latice relaxation time (Ti) can be determined by the inversion recovery technique. The echo signal grows exponentially with time r between the pulses as... 

Here we will summarize the reaction steps that lead to sihca gel formation, and focus on the physical chemistry of the aging processes. NMR proton spin—latice relaxation measurements can be used to follow the morphological changes that occm in a silica gel as a function of time. Owing to the restricted movements and, hence, increased correlation times of the water molecules near to the silica-water interface, protons of water included in a porous solid have longer relaxation times than water in the bulk. A decrease in the spin-spin relaxation time is to be interpreted as an increase in the number of water molecules restricted in their movements due to the proximity of the sihca structure. Figure 9.20 shows the spin-spin relaxation for a silica system as a function of relaxation time. The decrease in Tg in the first 20 min of the reaction indicates the formation of increasing silica surfaces in contact with water. 

Fig. 15. Energy level diagram fisr the three lowest excited states of [Ru(bpy-hg)j] in (Zn(bpy-hglgKClOJz.The spin-latice relaxations (sir) from state 111) to the states II) and 11) are very fast,but the relaxation from state II) to 11) is hindered at T = 1.2 K, due to a slow process of direct phonon emission. This leads to a decay time of 220 10 ns [165,166], while the emission from state 11) decays with the usual emission lifetime of t, = 230 ps. Since the states II) and 11) are deactivated differendy by Franck-Condon (FC) and Herzberg-Teller (HT) vibrations, respectively, the emission spectra change distincdy with time (see Fig. 16). Similar properties are also observed for partially and per-deuterated [Rulbpylg] chromophores...

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