Theory of low temperature spin exchange scattering for a physisorbed two-dimensional gas of hydrogen atoms

Calculations are presented of the two-dimensional scattering cross sections which are required to evaluate the longitudinal and transverse relaxation times T 1 and T 2 and the frequency shift Δν due to spin exchange collisions between H atoms physisorbed on a surface. The results are used to interpret the recent measurements by Crampton and co-workers of the relaxation time T 1 for H atoms in the presence of solid H 2 walls. New results are also presented for T 1 , due to three-dimensional scattering in the gas, using a more recent triplet H–H potential than the one previously employed by Berlinsky and Shizgal.