Depolarization of excited Ne*(2p3p; J=1) atoms due to He atom collisions

In a temperature controlled glow discharge of a mixture of neon and helium gases at 77 and 292 K, a linearly polarized laser pulse produces polarized neon atoms on the 2p5 (in Paschen notation) level (atomic alignment) from the 1s3 level. We measure the direct fluorescence from the 2p5 level to the 1s2 level with its polarization components resolved. From the temporal evolution of the intensities for these components, we determine the disalignment rate. We report the rate coefficients due to helium-neon collisions determined from the dependence of the disalignment rate on the helium atom density. We compare our experimental rate coefficient with the theoretical value obtained from quantum close-coupling calculations based on the model potential for the Ne*(2p 5 3p)-He system proposed by Hennecart and Masnou-Seeuws in 1985, and find that the rate coefficients predicted by our calculations are about 90 % at 77 K and 60 % at 292 K larger than the experimental values. New calculations based on a modified model potential, which includes an additional static dipole polarizability term for the Ne*(2p5) atom to the model potential proposed by Hennecart and Masnou-Seeuws, show agreement with our experimental data within 30 % for both temperatures.