Pressure broadening and shift ofHe(23P0,1,2)−He(23S)lines

Abstract

The collisional broadening and shift of metastable helium fine-structure lines are calculated within the impact approximation. Ab initio Born-Oppenheimer potential energy curves correlating to $\mathrm{He}(1{}^{1}{S}_{0})$ and $\mathrm{He}(2{}^{3}{P}_{j})$ atomic levels are obtained using the configuration interaction valence bond method and combined with semiempirically calculated van der Waals interaction terms between these atoms to also study j-specific and j-changing collisions. A long-range van der Waals potential well exists in the ${}^{3}{\ensuremath{\Pi}}_{u}$ potential correlated to the $\mathrm{He}(1{}^{1}{S}_{0})+\mathrm{He}(2{}^{3}{P}_{j})$ limit, whose influence on the scattering phase shift is assessed. At $T=310\mathrm{K},$ the broadening and shift parameters are practically j independent and have average values of 12.60 and 1.87 MHz/Torr, respectively. The j-changing collisions have cross sections roughly five times smaller than the j-specific cross sections.