Disalignment rate coefficient of neon excited atoms due to helium atom collisions at low temperatures

Disalignment of neon excited atoms in the fine-structure 2p(i) levels (in Paschen notation) of the 2p(5)3p configuration is investigated in a helium-neon glow discharge at temperatures between 15 and 77 K;l At several temperatures, we plot the disalignment rate as a function of the helium atom density for Ne*(2p(2) or 2p(7)) + He(1s(2)) 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-Seeums (19, 851 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.