Longitudinal Relaxation Time Measurements in Hydrogen Gas at Low Densities

Abstract

Measurements of the nuclear spin longitudinal relaxation time through the region of the characteristic minimum at 49.0 MHz in molecular hydrogen are reported at 77.5, 296, and 385 K. At 77 K molecular hydrogen may be treated as a single J-level quantum system. The experimental measurements serve to check the basic approximations in the Bloom–Oppenheim relaxation theory. The present data show that the ratio τsr/τd of the correlation times associated with the spin–rotation and dipolar interactions lies in the range from 0.58 to 0.83; the theoretical prediction is 0.6. At 296 and 385 K molecular hydrogen may be treated as a two J-level quantum system. Starting from the Bloom–Oppenheim theory it is possible to express the contribution to the transition rate from collisions which cause transitions between the J states to that which causes transitions within a J manifold in terms of a parameter R. The present experiments are consistent with R values in the ranges 1 < R < 10 at 296 K and 0.6 < R < 20 at 385 K.