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.

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

1972 ◽  
Vol 50 (12) ◽  
pp. 1252-1261 ◽  
Author(s):  
James A. Courtney ◽  
Robin L. Armstrong
Keyword(s):  
Lattice Relaxation ◽  
Relaxation Mechanism ◽  
Lattice Relaxation Time ◽  
Spin Rotation ◽  
Spin Lattice Relaxation ◽  
Molecular Reorientation ◽  
Effective Spin ◽  
Spin Lattice ◽  
Pass Through ◽  
Rotation Constant

The spin–lattice relaxation time T1 of the 19F nuclei was measured in gaseous samples of CF4, SiF4, GeF4, and SF6 at room temperature for densities from 0.015 to 20 amagat. In each case T1 was observed to pass through a minimum for some density less than 0.50 amagat. In addition, T1 was measured in the extreme narrowing region for SF6 at 238, 265, 293, 313, and 349.5 K.. 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. Assuming the validity of the model used to analyze the relaxation data, the combination of nuclear magnetic relaxation results with molecular beam measurements yields more accurate values of the anisotropic spin–rotation constant Cd than have been previously available.

Molecular Reorientation in the Plastic Crystalline Phase of Tris

1979 ◽  
Vol 32 (4) ◽  
pp. 905 ◽  
Author(s):  
RE Wasylishen ◽  
PF Barron ◽  
DM Doddrell
Keyword(s):  
Phase Transition ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Molecular Reorientation ◽  
Liquid Phase Transition ◽  
X Ray ◽  
Spin Lattice

Carbon-13 N.M.R. spectra of tris(hydroxymethyl)aminomethane (Tris) have been measured between 407 and 461 K. Proton-decoupled 13C N.M.R. spectra of solid Tris between 407 K and its melting point are relatively sharp (v� < 30 Hz) indicating rapid overall molecular reorientation in this temperature range. It was not possible to detect a 13C N.M.R, signal for Tris below 407 K. The observed 13C N.M.R. spin-lattice relaxation times appear continuous across the solid ↔ liquid phase transition. From the temperature dependence of T1, a rotational activation energy of 51.6 � 6 kJ mol-1 is calculated, which indicates that the molecules must expend considerable energy in reorienting. The N.M.R. results are discussed in relation to previous differential scanning calorimetry and X-ray diffraction data which indicate that Tris undergoes a solid ↔ solid transition at 407 K.

scholarly journals Spin-Gitter-Relaxationszeit T1 von Nitrilkohlenstoffen / Spin-Lattice-Relaxation Time T1 of Nitrile Carbon-atoms

1979 ◽  
Vol 34 (3) ◽  
pp. 375-379 ◽  
Author(s):  
H. Sterk ◽  
J. Kalcher ◽  
G. Kollenz ◽  
H. Waldenberger
Keyword(s):  
Relaxation Time ◽  
Correlation Time ◽  
Lattice Relaxation ◽  
Relaxation Mechanism ◽  
Lattice Relaxation Time ◽  
Spin Rotation ◽  
Spin Lattice Relaxation ◽  
Hydrogen Atoms ◽  
Spin Lattice ◽  
Almost All

Abstract It is shown that in almost all nitrile carbon-atoms T1 depends first of all on the inter-and/or intramolecular dipol-dipol-relaxation mechanism. Only acetonitrile, as is already known, shows a remarkable dependence on the spin-rotation-relaxation mechanism. This influence is strongly decreasing with an increasing number of atoms, specially hydrogen atoms, in the molecule. The significance of the correlation time r is discussed extensively and the experimental results are verified by calculation of T1 using the viscosity and the inertial moments as parameters.

Quadrupolar Relaxation of X Type Nuclei in R2MX6 and RMX3 Compounds

1975 ◽  
Vol 53 (12) ◽  
pp. 1141-1147 ◽  
Author(s):  
Henry M. van Driel ◽  
Robin L. Armstrong
Keyword(s):  
Relaxation Times ◽  
Lattice Relaxation ◽  
Relaxation Mechanism ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Mode Spectrum ◽  
Spin Lattice ◽  
Raman Process ◽  
Quadrupole Resonance ◽  
Quadrupolar Relaxation

Calculations of nuclear quadrupolar spin–lattice relaxation times are presented. The expressions obtained for the first order Raman and anharmonic Raman processes are applicable to a pure nuclear quadrupole resonance investigation of the X nuclei in R2MX6 and RMX3 solids. On the basis of realistic assumptions it is shown that the anharmonic Raman process will provide the dominant relaxation mechanism for these nuclei in these compounds. The relation between the spin–lattice relaxation time and the lattice dynamics is obtained explicitly without recourse to an assumed form of lattice vibrational normal mode spectrum. In favorable cases it is shown that the spin–lattice relaxation times can be related to Brillouin zone averaged rotary mode frequencies which are useful for the analysis of experimental data.

13C and 2H spin–lattice relaxation in neopentane-d12

1978 ◽  
Vol 56 (19) ◽  
pp. 2576-2581 ◽  
Author(s):  
Brian A. Pettitt ◽  
Roderick E. Wasylishen ◽  
Ronald Y. Donc ◽  
T. Phil Pitner
Keyword(s):  
Melting Point ◽  
Variable Temperature ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Rotation ◽  
Coupling Constants ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Single Temperature ◽  
Momentum Correlation

The results of a variable temperature study of the 2H and 13C spin–lattice relaxation times in neopentane-d12 are reported. along with those for the 13C's in neopentane at a single temperature. Orientational and angular momentum correlation times derived from these T1's exhibit the following: (i) τ2 is continuous through the melting point with an activation energy of 0.98 kcal/mol, (ii) τJ is more or less constant at 0.33 ± 0.03 ps within 40 K of either side of the melting point, and (iii) they do not conform to the theoretical relationships of extended diffusion, Fokker–Planck, or Langevin theories. The spin–rotation coupling constants are calculated to be −0.69 kHz for neopentane and −0.52 kHz for neopentane-d12

A nuclear magnetic resonance study of 1H, 23Na, and 31P relaxation and molecular dynamics in the sodium salts of some pyrophosphates

1989 ◽  
Vol 67 (6) ◽  
pp. 592-598 ◽  
Author(s):  
E. C. Reynhardt
Keyword(s):  
Relaxation Times ◽  
Lattice Relaxation ◽  
Laboratory Frame ◽  
Nuclear Magnetic Resonance Study ◽  
Spin Lattice Relaxation ◽  
Molecular Reorientation ◽  
Temperature Range ◽  
Spin Lattice ◽  
Second Moments ◽  
31P Relaxation

Proton second moments and spin-lattice relaxation times in the laboratory and rotating frames and 31P and 23Na spin-lattice relaxation times in the laboratory frame have been measured over the temperature region 295 > T > 100 K for the sodium pyrophosphate salts, Na2P2O7∙10H2O and Na2H2P2O7. Laboratory-frame 31P and 23Na spin-lattice relaxation times have also been measured over the same temperature range for Na4P2O7. In the case of Na4P2O7∙10H2O, the results show clearly that the H2O molecules execute a twofold jump motion at higher temperatures. The potential barriers to these motions range from 30 to 40 kJ/mol. The 31P and 23Na relaxations are also influenced by these motions. The [Formula: see text] ion in Na2H2P2O7 is stationary over the temperature range studied. T1(Na) is most probably dominated by acoustical lattice vibrations. The [Formula: see text] ion in Na4P2O7 is not involved in a molecular reorientation. A shallow T1(P) minimum of 55 s is associated with a limited motion of the pyrophosphate molecule.

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.

Proton and Fluorine-Spin-Lattice Relaxation in Poly crystalline FeSiF6 • 6 H2O

1981 ◽  
Vol 36 (6) ◽  
pp. 637-642 ◽  
Author(s):  
H. Rager
Keyword(s):  
Sharp Increase ◽  
Relaxation Times ◽  
Larmor Frequency ◽  
Lattice Relaxation ◽  
Relaxation Mechanism ◽  
Spin Lattice Relaxation ◽  
Temperature Range ◽  
Spin Lattice ◽  
Nuclear Spin Lattice Relaxation ◽  
Standard Pulse

Abstract The proton and fluorine nuclear spin-lattice relaxation has been measured in FeSiF6 • 6H2O in the temperature range 130 K ≦ T ≦ 420 K with standard pulse methods at 30 MHz. The relaxation times, T1(1H) and T1(19F), decrease with decreasing temperature according to the expression T1=a(I)exp(-Δ/T) (I = 1H, 19F). They show no significant dependence on the Larmor frequency. Thus, the unpaired Fe2+ electrons are mainly responsible for the proton and fluorine spin-lattice relaxation. The relaxation mechanism is described by an Orbach process. The ratio T1(19F)/T1(1H) is relatively constant over the whole temperature range investigated. This is explained by the strong H ... F bonds in FeSiF6 · 6H2O. The sharp increase of T1(1H) and T1(19F) at 224 K is attributed to the phase transition, which probably alters the crystal field at the Fe2+ centers

Nuclear Magnetic Resonance Studies of Molecular Motion in a Number of Stearates and Oleates

1971 ◽  
Vol 49 (5) ◽  
pp. 731-739 ◽  
Author(s):  
J. A. Ripmeester ◽  
B. A. Dunell
Keyword(s):  
Phase Transition ◽  
Alkali Metal ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Relaxation Mechanism ◽  
Spin Lattice Relaxation ◽  
Relaxation Processes ◽  
Lower Phase ◽  
Spin Lattice ◽  
Significant Difference

The broad line p.m.r. spectra of the alkali metal oleates have been observed from 77 °K up to or beyond the crystalline to waxy phase transition. Lower phase transition temperatures are observed in the oleates than in the stearates. This fact is attributed to larger entropies of transition in the oleates than in the stearates. The n.m.r. second moments indicate that in the stearates the packing of chains is probably not closer than in the oleates and consequently that the barriers to chain reorientation are not significantly higher in the stearates than in the oleates. Sodium oleate and stearate both appear to behave irregularly in the series of alkali metal soaps. Spin-lattice relaxation times have been measured by adiabatic rapid passage methods for both alkali metal oleates and stearates. Values of T1 and of the activation energy barrier for the reorientation of end methyl groups are compared with values obtained by other workers. No significant difference is seen between relaxation processes in stearates and oleates, at least in the lower temperature range. Soaps which seem to have some amorphous character have a second relaxation mechanism, in addition to end methyl group rotation, which is evidently important in the region of about 150–250 °K.

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