Effects of Off-Resonance Irradiation, Cross-Relaxation, and Chemical Exchange on Steady-State Magnetization and Effective Spin–Lattice Relaxation Times

2000 ◽  
Vol 143 (2) ◽  
pp. 360-375 ◽  
Author(s):  
Peter B Kingsley ◽  
W.Gordon Monahan
Keyword(s):  
Steady State ◽  
Chemical Exchange ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Cross Relaxation ◽  
Spin Lattice Relaxation ◽  
Effective Spin ◽  
Spin Lattice

A Nuclear Spin Relaxation Study of the Spin–Rotation Interaction in Symmetric Top Molecules

1972 ◽  
Vol 50 (12) ◽  
pp. 1262-1272 ◽  
Author(s):  
Robin L. Armstrong ◽  
James A. Courtney
Keyword(s):  
Relaxation Times ◽  
Lattice Relaxation ◽  
Relaxation Mechanism ◽  
Spin Rotation ◽  
Spin Lattice Relaxation ◽  
Molecular Reorientation ◽  
Effective Spin ◽  
Spin Lattice ◽  
Simple Exponential Function ◽  
Symmetric Top Molecules

The spin–lattice relaxation times T1 of 1H, 19F, and 31P nuclei were measured in gaseous samples of BF3, CHF3, CH3F, PH3, and NH3 at room temperature for densities from 0.03 to 10 amagat. In several cases the behavior of T1 at the lowest densities snowed deviations from the linear variation characteristic of the extreme narrowing region. The spin–rotation interaction provides the dominant relaxation mechanism in all cases. The data are analyzed on the basis of the assumption that the collision modulated spin–rotation interaction may be described by a single correlation function which is a simple exponential function of time. Values of an effective spin–rotation constant and a cross section for molecular reorientation are obtained for each gas. The results obtained are compared with those available from other types of experiments. This comparison indicates that the theory for spin–lattice relaxation in dilute gases of symmetric top molecules needs to be carefully reassessed.

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.

SPIN–LATTICE RELAXATION EFFECTS OBSERVED IN THE CONTINUOUS POWER SATURATION OF PARAMAGNETIC LINES

1960 ◽  
Vol 38 (3) ◽  
pp. 495-503 ◽  
Author(s):  
G. V. Marr ◽  
Prem Swarup
Keyword(s):  
Transition Probability ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Pulse Technique ◽  
Effective Spin ◽  
Spin Lattice ◽  
Relaxation Effects ◽  
Continuous Power ◽  
Photon Interactions

The dependence of the conventional saturation parameter on the incident microwave power is considered for Lorentzian-shaped paramagnetic lines and applied to a study of the [Formula: see text] transitions of Cr+++ in K3Co(CN)6 and Gd+++ in La(C2H5SO4)3∙9H2O at 9 kMc/sec and 4.2 °K. It is shown that the experimental observations may be explained on the basis of a spin–lattice transition probability which depends on spin–photon interactions. Values of the effective spin–lattice relaxation times are compared with pulse technique determinations and estimates of the corresponding phonon relaxation times are also given.

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