Proton Spin–lattice Relaxation in Polyatomic Gases

Abstract

The proton spin–lattice relaxation time T1 has been measured in gaseous samples of methane, ethylene, and ethane as a function of pressure at room temperature and also at 193° K for methane. In the pure gases T1 is proportional to density, p, at low densities indicating that intramolecular interactions couple the spin systems to the lattice, as is the case in hydrogen gas. T1/p at low densities gives information on the mean square angle through which the molecules are rotated per collision. Relaxation due to paramagnetic O2 is observed at higher densities when oxygen gas is added as an impurity. The relaxation probability per collision with an oxygen molecule is about 5 times larger for the ethylene–oxygen system than for the other two systems studied. This anomaly is discussed in terms of the theory of Oppenheim and Bloom. It is shown that a study of the temperature dependence of T1 due to O2 impurities provides a new way of obtaining detailed information on the Lennard–Jones parameters for the interaction between O2 and the solvent molecules.

Combined Nuclear Magnetic Resonance and Molecular Dynamics Study of Methane Adsorption in M2(dobdc) Metal–Organic Frameworks

“…NMR studies of the relaxation of gas-phase methane inform our analysis because these data exhibit a maximum in relaxation with changing density, albeit at 193 K. 52 At low methane density the relaxation rate correlates with the number of binary collisions; 47 as the collision frequency increases with pressure, molecular impacts perturb the rotational angular momentum, effectively shortening the rotational correlation time and leading to a maximum in the spin−lattice relaxation rate (R 1 ) as the nuclear Larmor frequency and the collision frequency become equal. At higher pressures, the observed R 1 decreases linearly with the gas density because of further shortening of the rotational correlation time.…”

Calculation of the transport and relaxation properties of methane. II. Thermal conductivity, thermomagnetic effects, volume viscosity, and nuclear-spin relaxation

“…Bloom et al 26 measured the relaxation of the proton spins in methane for temperatures between 100 K and 300 K. These measurements were complemented by Lalita and Bloom 67 , who covered the temperature range from room temperature to 700 K. They noted that their expression for the cross section as a function of temperature was consistent with earlier measurements at or below room temperature. 25,26,68,69 Other measurements at temperatures of 194.75 K, 273.15 K, and 298.15 K were reported at about the same time by Gerritsma et al 71 For these we have employed the values at the lowest number density for which results are reported. Jameson et al 28 repeated the measurements of proton spin relaxation and extended these measurements to the relaxation of the 13 C nuclear spin in 13 CH 4 , for temperatures between 230 K and 400 K. The analogous spin-rotation relaxation mechanism applies.…”

NMR Spin-Lock Induced Crossing (SLIC) dispersion and long-lived spin states of gaseous propane at low magnetic field (0.05 T)

“…41 Secondly, the dominant relaxation mechanism for molecules in the gas phase is often the modulation of spin-rotation interactions rather than dipole-dipole interactions, because dipole-dipole interactions are effectively “switched off” between spins in a singlet state. 42-43 Nevertheless, it has been shown theoretically 44-45 and experimentally 45-47 that LLSS can exist in multi-spin systems comprising more than two coupled spins.…”