Line profile of H Lyman-β emission from dissociative excitation ofH2

A high-resolution ultraviolet spectrometer was employed for a measurement of the H Lyman-β (H ${\mathrm{L}}_{\mathrm{\beta }}$) emission Doppler line profile at 1025.7 Å from dissociative excitation of ${\mathrm{H}}_2$ by electron impact. Analysis of the deconvolved line profile reveals the existence of a narrow central peak, less than 30 mÅ full width at half maximum (FWHM), and a broad pedestal base about 260 mÅ FWHM. Analysis of the red wing of the line profile is complicated by a group of Werner and Lyman rotational lines 160–220 mÅ from the line center. Analysis of the blue wing of the line profile gives the kinetic-energy distribution. There are two main kinetic-energy components to the H(3p) distribution: (1) a slow distribution with a peak value near 0 eV from singly excited states, and (2) a fast distribution with a peak contribution near 7 eV from doubly excited states. Using two different techniques, the absolute cross section of H ${\mathrm{L}}_{\mathrm{\beta }}$ is found to be 3.2±0.8×${10}^{\mathrm{-}19}$ ${\mathrm{cm}}^2$ at 100-eV electron impact energy. The experimental cross-section and line-profile results can be compared to previous studies of Hα (6563.7 Å) for principal quantum number n=3 and ${\mathrm{L}}_{\mathrm{\alpha }}$ (1215.7 Å) for n=2. © 1996 The American Physical Society.