Spin-lattice relaxation with inversion recovery

The technique for measurement which is most easily interpreted is the inversion-recovery method, in which the distribution of the nuclear spins among the energy levels is inverted by means of a suitable 180° radiofrequency pulse A negative signal is observed at first, which becomes increasingly positive with time (and hence also with increasing spin-lattice relaxation) and which... 

FIGURE 31. Typical data set for measurement of the spin-lattice relaxation times of the sp2-hybridized carbon atoms of, 6-carotene at 11.7 T. The chemical shift values are shown across the bottom of the figure. The t-value for each spectrum is the delay time in the inversion-recovery pulse sequence. Reprinted with permission from Reference 49. Copyright (1995) American Chemical Society... 

Spin-lattice relaxation times were measured by the fast inversion-recovery method (24) with subsequent data analysis by a non-linear three parameter least squares fitting routine. (25) Nuclear Overhauser enhancement factors were measured using a gated decoupling technique with the period between the end of the data acquisition and the next 90° pulse equal to eibout four times the value. Most of the data used a delay of eibout ten times the Ti value. (26)... 

Polymer Dynamics. 13C spin-lattice relaxation times (Ti) were determined with either an inversion-recovery sequence (16) (for carbons observed by direct polarization) or with a modified cross-polarization experiment (17). 13C rotating-frame relaxation times (Tip(C)) were derived from measurements of the carbon signal that remained after a Tjp(C) hold time of... 

Fig. 2.30. Determination of 13C spin-lattice relaxation times by inversion-recovery (a), progressive saturation (b), and comparative evaluation of the intensities (c) values from (a) with full, from (b) with empty characters, abscissa on top for C-2, abscissa on bottom for C-1 and C-3) sample propynol, 75% by vol. in hexadeuterioacetone. 25 C, not degassed, 15.08 MHz, 10 scans/ experiment in (a),...

Fig. 4.15. Inversion-recovery experiment for carbon-13 7, determination or2,2 -bipyridine (400 mg in 1 mL hexadeuteriobenzene, 30 °C 15.08 MHz 16 scans for a single experiment [73 i]). The principal axis of (the fastest) molecular rotation passes C-2 (2 ) and C-5 (5 ). This rotation is too fast for optimum dipolar relaxation of C-3, C-4, and C-6 but does not influence the C-5-H bond which is affected by rotation about other axes. These rotations are slower and more effectively contribute to dipolar spin-lattice relaxation of C-5 (5 ) according to Section 3.3.3.3. To conclude, C-5 (5 ) relaxes faster (3 s) than all other CH carbons (6 s) and can be clearly distinguished from C-3 (3 ) with similar shift.

In order to determine the content of this noncrystalline line further, we examined in more detail the behavior of the spin-lattice relaxation. Figure 5 shows the partially relaxed spectra in the course of the inversion recovery pulse sequence (180°-t-90°-FIDdd-10s)i2o with varying x values. The magnetization that was recovered for 10 s in the z direction was turned to negative z direction by 180° pulse and the magnetization recovered in z direction for varying x was measured in the xy plane under H DD. The spectra at different steps of the longitudinal relaxation were obtained by Fourier transform and are shown in Fig. 5. In these spectra the contribution from the crystalline components with Tic s of2,560 and 263 s are eliminated due to the lack of time for recovery at each pulse sequence. Therefore, we observed preferentially the relaxation process of the noncrys-... 

By using the inversion recovery method with the standard pulse sequence (180°-t-90°-T), it is possible to determine the spin-lattice relaxation times in the supercritical state. The values of benzyl-n-butylphthalate have been... 

Relaxation parameters provide valuable information about molecular motions. The spin-lattice relaxation time T is usually determined by the so-called inversion recovery pulse sequence (65). The experiment comprises a set of spectra with different interpulse delays, and Tx is determined by fitting the signal intensities for a given nucleus to Eq. 2, where A and B are constants, x is the respective interpulse delay, and /,is the intensity measured at that delay ... 

FIGURE 51. Measurement of 29Si spin-lattice relaxation time in 1,1,3,3-tetramethyldisilazane using conventional inversion-recovery (top, measuring time 6.5 h, T = 37.6 1.4 s) and INEPT enhanced version (bottom, measuring time 45 min, T = 38.1 0.9 s) with the phase of penultimate proton pulse +y. Reproduced by permission of Academic Press from Reference 357... 

Theoretical expressions for spin-lattice relaxation of 2H nuclei (determined by locally axially symmetric quadrupolar interactions modulated by molecular motions) can be derived for specific dynamic processes, allowing the correct dynamic model to be established by comparison of theoretical and experimental results [34,35]. In addition, T, anisotropy effects, which can be revealed using a modified inversion recovery experiment, can also be informative with regard to establishing the dynamic model [34,35]. 

The spin-lattice rehucation times Ti are measured by the inversion-recovery method By the capillary method, we have measured the spin-lattice relaxation times Tj for heavy water (D2Q) over a wide range of temperature. The results are in good agreement with those given by Hindman and co-workers - within the expe ental uncertainties our and their uncertainties ate 1% and 12%, respectively. The uncertainty of tempm ture is 0.1 C in the present work. 

Spin-lattice relaxation times for the carbon atoms of L-ascorbic acid treated with Chelex-100 (Bio-Rad Laboratories) were determined on 0.25 M solutions in deuterium oxide purged with nitrogen. The inversion-recovery method (33-35) with alternating phases and 8-10 t values was used for the protonated carbons, and the homo-spoil technique with 6-8 t values was used for the non-protonated atoms. The spin-lattice relaxation times (Tj) were calculated from the data using the appropriate Nicolet (25) digital computer programs. The Ti-values for the nonprotonated carbon atoms were repeated using the inversion recovery method and were virtually identical to those reported in Table 1. 

Measured via cross polarization, with inversion-recovery, at the frequency indicated. Only one proton spin-lattice relaxation... 

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