The effect of van der Waals complexes on the longitudinal proton spin relaxation time in hydrogen–argon gas mixtures

Publisher Website
Google Scholar
Abstract
An extensive set of measurements of the proton spin longitudinal relaxation time T1 for molecular hydrogen diluted in argon is presented. These measurements, carried out at 18.975 MHz, establish the temperature and density dependence of the relaxation time from 110 to 300 K and from 2 to 100 amagat, respectively. The T1 data, although taken in the intermediate density regime in which binary collisions lead to a characteristic linear dependence on density, ρ, exhibit a significant nonlinear dependence. This effect is attributed to the presence of van der Waals complexes (H2–Ar dimers) in the mixture and is explained as a consequence of the formation and annihilation dynamics of the dimers. A theoretical model is developed which accounts for all qualitative aspects of the data. The dimer contribution to the relaxation time is described in terms of two parameters: the dimer annihilation cross section σ and the equilibrium constant K describing the relative number of H2–Ar dimers. The cross section σ is very nearly equal to the geometric cross section. The constant K is of the order of 10−23 cm3 and in good agreement with the theoretical value. Its variation with temperature is predicted well by our calculations.

This publication has 0 references indexed in Scilit: