Disalignment rates of the neon 2p[5] and 2p[10] atoms due to helium atom collisions measured at temperatures between 77 and 294 K

Abstract

Using a positive column of helium–neon glow discharge plasma at several temperatures between 77 and 294 K, the disalignment rates of excited neon atoms in the 2p[5] and 2p[10] (in Paschen notation) levels are measured by a polarization-resolved laser-induced fluorescence technique. For the 2p[10] case, the disalignment rate due to radiation reabsorption is evaluated from the optical thickness of the plasma measured by a self-absorption method, and then is subtracted from the disalignment rate measured. From the slope of the obtained disalignment rate plotted against the helium atom density we determine the rate coefficients due to helium atom collisions. These rate coefficients are compared with the results of quantum multi-channel close-coupling calculations using the modified long-range potentials proposed by Bahrim and Khadilkar (2009 Phys. Rev. A 79 042715) from the original potentials of Hennecart and Masnou-Seeuws (1985 J. Phys. B: At. Mol. Phys. 18 657). Our present experiment agrees excellently with the theory for the 2p[5] level at any temperatures between 77 and 294 K, and for the 2p[10] state only at 294 K. Below 294 K, the experimental rate coefficients for the 2p[10] state show a more rapid decrease with the decrease in temperature than the theory predicts.