EGAS41 - Swansea University

41 st EGAS CP 6 Gdańsk 2009
Experimental Stark broadening studies of the OI multiplet
3p 5 P−3d 5 D o at 9264 Å.
A. Bartecka ∗ , A. Bac̷lawski and J. Musielok
Institute of Physics, Opole University, ul. Oleska 48, 45-052 Opole, Poland
∗ Corresponding author: bartecka@uni.opole.pl,
A high current wall-stabilized arc with flat carbon electrodes, operated at atmospheric
pressure in helium and argon, with small admixture of oxygen and hydrogen was applied
as excitation source of the studied spectra. The radiation of the plasma emitted from
nearly homogeneous plasma layers in end-on direction was detected by applying a grating
spectrometer equipped with a CCD detector. This instrumentation provides spectra with
a reciprocal dispersion of 0.043 Å/pixel. The apparatus profile was determined by applying
low-pressure krypton- and neon-discharge lamps of a Plücker type, which were also used
as standard sources for wavelength calibration. At the entrance slit – 26 µm of the
spectrometer, the apparatus profile is of Gaussian type with a FWHM of 0.08 Å. The
radiance calibration was carried out against light outputs originating form a tungsten
strip radiation standard.
The arc current was varied from 31 to 54 A in order to obtain different plasma conditions:
electron densities from the range 2.5·10 21 − 1.4·10 22 m −3 , corresponding to electron
temperatures between 10000 and 13700 K. The electron density N e was determined
from measured FWHM of the hydrogen H β line and using theoretical broadening data of
Gigosos and Cardeñoso [1]. The plasma temperature T e was determined by measuring
total line intensities of three infrared OI multiplets (at 7773 Å, 8820 Å, 9264 Å) and applying
the standard Boltzmann plot method. The transition probability data have been
taken from NIST Atomic Spectra Database [2].
The multiplet 3p 5 P−3d 5 D o consists of nine fine structure components. Because of
the small differences in wavelengths between spectral lines involving the same lower level,
this multiplet appears – at our plasma conditions and spectral resolution – in form of
three spectral features, each consisting of three fine structure components.
Spectral lines of neutral atoms emitted from plasmas are usually affected by a few
broadening mechanisms. In the case of non-hydrogenic transitions the main contribution
arises from collisions between emitters and fast moving electrons, producing shifted
Lorentzian-like line shapes. Collisions with ions lead to some additional broadening and
cause an asymmetry of the profile. Such profiles can be described by an asymmetric
so-called j(x) function introduced by Griem [3, 4]. These j(x) profiles convoluted with
the corresponding Doppler and apparatus profiles were fitted to our experimental data.
In this way the electron impact widths of fine structure components of the investigated
multiplet were determined. The evaluated Stark broadening parameters are compared
with theoretical data of H.R. Griem [4].
References
[1] M.A. Gigosos, V. Cardeñoso, J. Phys. B 29, 4795 (1996)
[2] http://physics.nist.gov/PhysRefData/ASD/index.html
[3] H.R. Griem Spectral line broadening by plasmas (Academic Press, New York 1974)
[4] H.R. Griem Plasma Spectroscopy (McGraw-Hill, New York 1964)
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