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We calculate the 3Se and 1Se scattering lengths in low-energy e- + Rb(5s), Cs(6s), and Fr(7s) collisions. Our approach is based on the relativistic version of the modified effective range theory (MERT) and extrapolates eigenphases provided by Dirac R-matrix calculations to zero energy. To test the accuracy of our MERT extrapolation method, we compare the fine-structure components for the lowest 3Po resonance of Fr- ion with full Dirac R-matrix calculations.

Our Dirac R-matrix calculations suggest that none of the heavy alkali-metal negative ions, Rb, Cs, and Fr, has an excited bound state. Their lowest excited state appears to be a multiplet of 3 P J o -shape resonances, the Jϭ1 component of which was recently observed in photodetachment experiments on Cs Ϫ . We analyze these 3 P J o and the 3 S e excited negative ion states in partial and converged total scattering cross sections for slow electrons with incident kinetic energies below 120 meV. Our results are in excellent agreement with available experimental data. We also propose a new value for the electron affinity of Fr, provide the scattering length for electronic collisions with Rb, Cs, and Fr, and discuss the nuclear charge dependence of relativistic effects in the resonance profiles.

Disalignment of neon excited atoms in the fine-structure 2pi levels (in Paschen notation) of the 2p53p configuration is investigated in a helium–neon glow discharge at temperatures between 15 and 77 K. At several temperatures, we plot the disalignment rate as a function of the helium atom density for Ne∗ (2p2 or 2p7) + He(1s2) collisions. The slope of this dependence gives the disalignment rate coefficient. For both collisions, the experimental data for the disalignment rate coefficient show a more rapid decrease with the decrease in temperature below 40 K than our quantum close-coupling calculations based on the model potential of Hennecart and Masnou-Seeuws (1985 J. Phys. B: At. Mol. Phys. 18 657). This finding suggests that the disalignment cross section rapidly decreases below a few millielectronvolts, in disagreement with our theoretical quantum calculations which predict a strong increase below 1 meV. The disagreement suggests that the long-range electrostatic potentials are significantly more repulsive than in the aforementioned model.