Stark parameters of neutral helium 318.8 nm line

Departamento de Física Teórica, Atómica y Óptica, Universidad de Valladolid, 47071 Valladolid, Spain e-mail: apa@opt.uva.es

Received: 15 December 2005
Accepted: 2 March 2006

Abstract

Aims.Our aims is to measure with good accuracy the Stark parameters (width and shift) of the He I 318.8 nm (2s S-4p P) line and to calibrate Stark width and shift dependencies of this line as a function of the electron density. In this way, it is possible to obtain an alternative method of diagnosing the plasmas of astrophysical origin and to check the quality of theoretical models that predict these parameters.

Methods.We made a spectroscopic and interferometric analysis of a pulsed plasma. The electron temperature was obtained with an intensity ratio of He II lines and ranges from 19 000 to 23 000 K. Electron density was determined by interferometry ranging from  m^-3 to  m^-3.

Results.These experimental results are new for these plasma conditions. When joined with previous bibliographic data, they allowed us to obtain an empirical calibration expression for the Stark width and the shift of this line in a broad range of electron densities. Comparisons with different theoretical models are also included.