Nuclear spin relaxation in compressed nitrogen gas

Abstract

Measurements of the 14N spin relaxation in compressed nitrogen gas are presented for temperatures of 145, 200, 293, and 380 °K and for pressures spanning the range from 50 to 1700 atm. In all cases the recovery of the nuclear magnetization following saturation is describable by a single time constant, T1. The corresponding dependence of T1 on the gas density ρ is deduced and, to first order, a linear relation is found with a temperature dependence given by [Formula: see text]. Applying the semiclassical theory of nuclear relaxation of Gordon, the effective cross section for molecular reorientation during a collision due to the intramolecular electric quadrupole interaction is deduced. The result is shown to be in reasonable agreement with the values deduced from studies of depolarized Rayleigh scattering and the Sentfleben-viscosity effect. The data is also discussed in terms of the Bloom theory of nuclear relaxation. It is assumed that the rotational correlation function can be written as the product of a free-molecule correlation function and a reduced correlation function that decays exponentially with time constant τ2. A theoretical expression for the dependence of T1 on τ2 is obtained. From a comparison of the equation with the data it is seen that, to a first approximation, [Formula: see text], where the τ2 values are of the order of 10−12 s.