Transport and Relaxation Phenomena in the Hydrogen Isotopes

Expressions are obtained for the collision cross sections governing the relaxation of angular momentum polarizations in the molecular hydrogen isotopes, making use of the fact that energetically inelastic collisions are very infrequent. A number of interrelationships between the collision cross sections of this type, occurring in NMR and in other transport and relaxation phenomena such as the Senftleben-Beenakker (SB) thermal conductivity effect, and depolarized Rayleigh light scattering, are developed and comparisons between calculated cross sections and those obtained from various experiments are given. For example, in $n$-${\mathrm{H}}_2$ at room temperature, the SB effect for the shear viscosity gives a characteristic cross section of (0.47 ± 0.05) ${\mathrm{\AA }}^2$ to be compared with a calculated cross section of 0.32 ${\mathrm{\AA }}^2$, and a cross section of 0.40 ${\mathrm{\AA }}^2$ which can be extracted from NMR measurements. A calculated value of ${\sigma }_{\mathrm{DPR}}$, for the cross section determining the width of the depolarized Rayleigh line, in $n$-${\mathrm{H}}_2$ of 0.48 Å, is obtained, to be compared with the experimental value 0.495 ${\mathrm{\AA }}^2$.