Theory of the Senftleben-Beenakker effects for NH3 and ND3: Collision integrals

The distorted wave Born approximation is used as a basis for understanding the cross sections which govern the production and relaxation of internal state polarizations, in gaseous ammonia, in the presence of shear flow or thermal gradients. For viscous flow, it is shown that the dominant dipole-dipole interaction leads to the production of [W](2)J polarization, but not to any appreciable [J](2) polarization. The essential absence of the usual [J](2) polarization, as produced by the anisotropic dispersion interaction (P2-potential), is consistent with the smallness of the anisotropy of the dipole polarizability in ammonia and with the suppression of the effect of such shorter ranged interactions (e.g. the P2 potential) in the presence of a dominant longer ranged interaction (there the dipole-dipole potential). For thermal conduction, it is shown that the dominant dipole-dipole interaction apparently produces predominantly a WJ(W2−52) polarization. The shorter ranged dipole-quadrupole interaction as well as higher multipole potentials produce a W[J](2) polarization, while a cross term between the dipole-dipole and quadrupole-dipole potentials can produce a velocity-independent dipolar polarization, denoted here as Jh1.