Inversion-recovery spin-lattice relaxation time

Figure 2.27. Sequence of measurements to determine the C spin-lattice relaxation times of 2-octanol (42) [(CD3)2C0, 75% v/v, 25 °C, 20 MHz, inversion-recovery sequence, stacked plot]. The times at which the signals pass through zero, xo, have been used to calculate, by equation 10, the T values shown above for the nuclei of 2-octanol...

Inversion recovery A pulse sequence used to determine spin-lattice relaxation times. 

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. 1. Pulse sequences for determining spin-lattice relaxation time constants. Thin bars represent tt/2 pulses and thick bars represent tt pulses, (a) The inversion-recovery sequence, (b) the INEPT-enhanced inversion recovery, (c) a two-dimensional proton-detected INEPT-enhanced sequence and (d) the CREPE sequence. T is the waiting period between individual scans. In (b) and (c), A is set to (1 /4) Jm and A is set to (1 /4) Jm to maximize the intensity of IH heteronuclei and to (1/8) Jm to maximize the intensity of IH2 spins. The phase cycling in (c) is as follows 4>i = 8(j/),8(-j/) 3 = -y,y A = 2(x),2(-x) Acq = X, 2 —x), X, —X, 2(x), —x, —x, 2(x), —x, x, 2 —x),x. The one-dimensional version of the proton-detected experiment can be obtained by omitting the f delay. In sequence (d), the phase 4> is chosen as increments of 27r/16 in a series of 16 experiments.

The NMR spectra were taken on a JEOL JNM-MH-100 (CW) spectrometer using tetramethylsilane as an internal standard. 13C spin-lattice relaxation time of the polymer was measured by the inversion-recovery Fourier transform method on a JNM-FX100 FT NMR spectrometer operating at 25 MHz. 

Spin-lattice relaxation times 7j of individual nuclei (13C, H) present in a molecule can be obtained by Fourier transformation of the FID signal following a 180°, r, 90° pulse sequence. The technique is referred to as inversion-recovery method [39, 40, 41] or... 

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),...

Finally, a coupled and decoupled 13C NMR spectrum of 2,2 -bipyrrole (Fig. 4.14(a,b) and an inversion-recovery series of 2,2 -bi pyridine (Fig. 4.15 [73 i]) illustrate signal assignments of heteroaromatic compounds by means of carbon-proton couplings and spin-lattice relaxation times. These spectra also exemplify the characteristic shift differences between n-excessive (2,2 -bipyrrole) and n-deficient heteroaromatic compounds (2,2 -bipyridine). 

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 10.5 compares the spin-lattice relaxation time (7)) obtained after inversion-recovery sequences of the APP/PER and the APP/PER-4A systems versus heat treatment temperature (HTT). At every HTT, only one 7) value was obtained and it can be therefore expected that the slow relaxation domains size will be smaller than 10 nm. 

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... 

The decay time constants for the polymeric radicals clearly vary from solvent to solvent, ranging over an order of magnitude from about 2 ps in tetrahydrofuran (THF) to 200 ns in methylene chloride. A similar solvent dependence of NMR Ti values has been reported by Spyros et al. They studied poly(naphthyl methacrylate) using the inversion recovery technique and found that the spin-lattice relaxation time of... 

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. 

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