Influence of cross-relaxation on NMR spin-lattice relaxation times

1973 ◽  
Vol 11 (2) ◽  
pp. 143-162 ◽  
Author(s):  
I.D Campbell ◽  
Ray Freeman
Keyword(s):  
Relaxation Times ◽  
Lattice Relaxation ◽  
Cross Relaxation ◽  
Spin Lattice Relaxation ◽  
Spin Lattice

Nitrogen-14 quadrupole cross-relaxation spectroscopy

1988 ◽  
Vol 416 (1850) ◽  
pp. 149-178 ◽  
Keyword(s):  
Magnetic Field ◽  
Double Resonance ◽  
Relaxation Times ◽  
High Sensitivity ◽  
Lattice Relaxation ◽  
Cross Relaxation ◽  
Spin Lattice Relaxation ◽  
Proton Relaxation ◽  
Spin Lattice ◽  
Quadrupole Resonance

Cross-relaxation spectroscopy can be used as a sensitive method of detecting 14 N quadrupole-resonance signals in hydrogen-containing solids. The 1 H spin system is polarized in a high magnetic field that is then reduced adiabatically to a much lower value satisfying the level­-crossing condition, when the 1 H Zeeman splitting matches one of the 14 N quadrupole splittings. If the 14 N spin–lattice relaxation time is much shorter than that of the 1 H nuclei, a drastic loss of 1 H polarization occurs that is measured by recording the residual 1 H magnetic resonance signal after the sample has been returned to the higher field. The experimental cycle can be run in several different ways according to the relative values of the 1 H spin–lattice relaxation times ( T 1 ) in high and low field, the 14 N spin–lattice relaxation ( T 1Q ) and cross-polarization times ( T CP ), all of which can markedly influence the spectra. The line shapes are broadened by the presence of the magnetic field and Zeeman shifts of the peak frequencies also occur, for which simple corrections may be derived. The methods used have high sensitivity, particularly if the ratio T 1 / T 1Q is large. They have the advantage over other double-resonance techniques in that long proton T 1 values are not necessary for the success of an experiment; it is also possible to select conditions in which the recovered 1 H signal is directly proportional to the relative numbers of 14 N nuclei present and the magnitude of the cross-relaxation field. Multi-proton relaxation jumps also give rise to signals at subharmonics of the fundamental, whose relative intensities reflect the extent to which the 14 N and 1 H relaxation is coupled via their dipole–dipole interactions, which are not completely quenched in the finite magnetic fields necessary in cross-relaxation spectroscopy. These conclusions are illustrated in a number of 14 N spectra of compounds in which quadrupole-resonance signals have not previously been recorded.

RELAXATION IN RUBY

1960 ◽  
Vol 38 (10) ◽  
pp. 1304-1317 ◽  
Author(s):  
R. A. Armstrong ◽  
A. Szabo
Keyword(s):  
Relaxation Time ◽  
Crystal Orientation ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Cross Relaxation ◽  
Spin Lattice Relaxation ◽  
Signal Frequency ◽  
Spin Lattice ◽  
A Value ◽  
Frequency Ratios

The relaxation of the (1↔2) and (2↔3) transitions in chrome-doped Al2O3 (0.015%) has been studied at S-band, using a pulsed microwave method, over a range of crystal orientations in the magnetic field at temperatures of 77 deg;K to 50 deg;K, and at 4.2 deg;K and 1.6 deg;K. A T−7 variation of the relaxation time with temperature was found in the liquid nitrogen range. The relaxation time in this temperature range was found to be independent of crystal orientation, and for the (1↔2) transition was 50 microseconds at 77 deg;K. At liquid helium temperatures, harmonic cross relaxation was present over most of the range of the crystal orientation studied and was observed at harmonic-to-signal frequency ratios of 2:1, 3:2, and 1:2. The harmonic cross relaxation times were typically 10 to 100 times shorter than the lattice relaxation times, and were independent of temperature. At non-harmonic points at 4.2 deg;K, the spin–lattice relaxation could be described by one time constant, a value of 300 milliseconds being typical. At harmonic points anomalously long relaxation times as high as 12 seconds were observed.

Bonded Hydrogen and Trapped H2 in a-Si1−xGex:H Alloys

1989 ◽  
Vol 149 ◽  
Author(s):  
E. J. Vanderheiden ◽  
G. A. Williams ◽  
P. C. Taylor ◽  
F. Finger ◽  
W. Fuhs
Keyword(s):  
Temperature Dependence ◽  
Molecular Hydrogen ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
H Nmr ◽  
Local Environments

ABSTRACT1H NMR has been employed to study the local environments of bonded hydrogen and trapped molecular hydrogen (H2) in a series of a-Si1−xGex:H alloys. There is a monotonic decrease of bonded hydrogen with increasing x from ≈ 10 at. % at x = 0 (a-Si:H) to ≈ 1 at. % at x = 1 (a-Ge:H). The amplitude of the broad 1H NMR line, which is attributed to clustered bonded hydrogen, decreases continuously across the system. The amplitude of the narrow 1H NMR line, which is attributed to bonded hydrogen essentially randomly distributed in the films, decreases as x increases from 0 to ≈ 0.2. From x = 0.2 to x ≈ 0.6 the amplitude of the narrow 1H NMR line is essentially constant, and for x ≥ 0.6 the amplitude decreases once again. The existence of trapped H2 molecules is inferred indirectly by their influence on the temperature dependence of the spin-lattice relaxation times, T1. Through T1, measurements it is determined that the trapped H2 concentration drops precipitously between x = 0.1 and x = 0.2, but is fairly constant for 0.2 ≤ x ≤ 0.6. For a-Si:H (x = 0) the H2 concentration is ≈ 0.1 at. %, while for x ≥ 0.2 the concentration of H2 is ≤ 0.02 at. %.

Water-Saturated Mesoporous MCM-41 Systems Characterized by 1H NMR Spin-Lattice Relaxation Times

1995 ◽  
Vol 99 (12) ◽  
pp. 4148-4154 ◽  
Author(s):  
Eddy Walther Hansen ◽  
Ralf Schmidt ◽  
Michael Stoecker ◽  
Duncan Akporiaye
Keyword(s):  
1H Nmr ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Water Saturated ◽  
Mcm 41
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