Production and relaxation cross sections for the shear viscosity SBE. II. IOSA results for the N2–He system

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Abstract
Infinite‐order sudden approximation (IOSA) calculations of the phenomenological production and relaxation cross sections governing the magnetoviscosity effect have been undertaken for the system N2 at infinite dilution in He for the purpose of testing the usefulness of the IOSA procedure. Three l‐labeling schemes (IL, FL, and AVL) have been employed and the results obtained for each of the three types of cross sections occuring in the viscomagnetic effect have been compared. For the relaxation cross sections σT( j′j‖Ek), σ(1)η( j′j‖Ek), and σ(2)η( j′j‖Ek), the IL/FL and AVL results differ by less than 5% on the average, but for the production cross sections σTη( j′j‖Ek), the three schemes IL, FL, AVL give widely differing results (one order of magnitude and sign). Thermally averaged phenomenological cross sections at 77.5 K were obtained for three potentials of the MSV type: one obtained from beam experiments and two using the beam scattering isotropic part and modified anisotropy parameters. For one of the modified anisotropic potentials giving reasonable agreement of the cross section σT calculated using the IOSA procedure and obtained from experiment, initial close‐coupled calculations were performed at a kinetic energy of 54 cm−1. The IOSA AVL procedure gave results for j, j′ = 1, 3 differing by as much as 30% for σT( j′j‖Ek), and σ(κ)η( j′j‖Ek) and by as much as a factor of 2 for σTη( j′j‖Ek). Tentatively, it appears that in order to calculate production cross sections with reasonable confidence and accuracy, it will be necessary either to modify the CSA and IOSA methods or to use the more accurate CC procedure.