Eur. Phys. J. D 23, 73-79 (2003)
https://doi.org/10.1140/epjd/e2003-00051-7

Cascade feeding of the 1s3d ³D level of He I from high-l states excited by proton impact

University of Gdańsk, Institute of Experimental Physics, ul. Wita Stwosza 57, 80-952 Gdańsk, Poland

Corresponding author: ^a fizrd@univ.gda.pl

Received: 15 October 2001
Revised: 26 July 2002
Published online: 4 March 2003

Abstract

The 1s3d ³D level of atomic helium cannot be excited directly by proton impact, but it is strongly populated by cascade feeding from 1snl states with , if  keV protons are used for excitation. This cascade feeding process can be analysed in detail by investigating the intensity of the spectral line at – nm as a function of an electric field directed parallel and antiparallel to the proton beam. In this paper the intensity functions are calculated assuming collisional excitation of parabolic singlet states  with large electric dipole moments. The theoretical results are compared with the experimental intensity function published earlier. Excellent agreement is obtained if the excitation cross-sections of the parabolic states scale as n^-3.