Spin–Lattice Relaxation and the Anisotropic Part of the He–H2 Intermolecular Potential

Proton spin-lattice relaxation times T1 were measured in mixtures of H2 with N2O as a function of density, composition, and temperature (200–400 K) in the region where [Formula: see text]. These data, along with the data obtained by Lalita and Bloom for H2–CO2, were interpreted, using Bloom–Oppenheim theory, to obtain the anisotropic intermoleeular potential parameters. Two models, (i) the Lennard–Jones (12–6) potential (LJP) and (ii) the modified Buckingham (exp-6) potential (MBP), were used to represent the isotropic part of the intermolecular potential. The relative anisotropy in the attractive r−6 term and the quadrupole moments of N2O and CO2 as obtained from MBP model are in better agreement with the values obtained from the polarizability data and the reported values, respectively, than those obtained from the LJP model.

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Librational motion in the α phase of solid nitrogen. III. Spin–Lattice relaxation

Canadian Journal of Physics ◽

10.1139/p77-225 ◽

1977 ◽

Vol 55 (21) ◽

pp. 1848-1857 ◽

Cited By ~ 3

Author(s):

Paul V. Dunmore ◽

D. A. Goodings

Keyword(s):

Single Molecule ◽

Lattice Relaxation ◽

Spin Lattice Relaxation ◽

Intermolecular Potential ◽

Spin Lattice ◽

Α Phase ◽

Solid Nitrogen ◽

Raman Process ◽

Librational Motion ◽

Quadrupolar Relaxation

The theory of spin–lattice relaxation of Van Kranendonk and Walker is adapted to the α phase of solid nitrogen. The quadrupolar relaxation of the 14N nucleus by the 'anharmonic Raman process' is calculated for the cubic anharmonic terms obtained from the theory presented in the first paper of this series. Different approximations to the Raich–Mills intermolecular potential are employed. When the expansion of the potential in spherical harmonics is truncated at l = 2, the calculated temperature dependence of T1 is in satisfactory agreement with the experimental measurements of DeReggi, Canepa, and Scott between 20 and 35 K. Below 15 K the calculated results for T1, are too long, probably due to the neglect of mixing between the librons and acoustic phonons. When the Raich–Mills potential includes the spherical harmonic terms with l = 4 and l = 6, the relaxation is found to increase by more than a factor of 40, resulting in T1, becoming much shorter than the experimental results over the high-temperature region. This arises mainly from single-molecule terms of three-fold symmetry in the potential, leading to the suspicion that these terms are unrealistically large.

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Intermolecular potentials from proton spin–lattice relaxation time in H2–Ar and H2–N2 gas mixtures

Canadian Journal of Physics ◽

10.1139/p81-164 ◽

1981 ◽

Vol 59 (9) ◽

pp. 1260-1266

Author(s):

Lakshman Pandey ◽

K. Lalita Sarkar

Keyword(s):

Spin Echo ◽

Relaxation Times ◽

Lattice Relaxation ◽

Gas Mixtures ◽

Lattice Relaxation Time ◽

Proton Spin ◽

Spin Lattice Relaxation ◽

Intermolecular Potential ◽

Intermolecular Potentials ◽

Spin Lattice

Proton spin-lattice relaxation times, T1, have been measured in H2–Ar and H2–N2 gas mixtures as a function of density (10 < ρ < 70 amagat), composition (~ 18–65%), and temperature (300–600 K) with a 30 MHz spin-echo spectrometer using phase sensitive detection. These data together with the T1 data obtained by Foster and Rugheimer and by Williams in these mixtures below 300 K have been analysed using the Bloom–Oppenheim theory. Models for intermolecular potentials to explain the T1 data have been proposed. It is found that the relative anisotropy in the attractive part of the intermolecular potential which fits the T1 data best compares well with that evaluated using polarizability data.

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