Improved and expanded measurements of transition probabilities in UV Ar ii spectral lines

Transition probabilities have a significant interest in the astrophysical field. The aim of this experiment is to extend the present data base of measured Ar ii transition probabilities to the ultraviolet (UV) region and to improve the quality of some of the already existing data. Despite all the efforts made to assemble an accurate set of transition probabilities (A ki), some of the data recommended by the National Institute of Standards and Technology (NIST) for Ar ii spectral lines in the UV region have uncertainties around 50 per cent. We measured relative intensities of spectral lines emitted from a low-pressure-pulsed discharge lamp which generates an argon plasma. Excitation temperatures of 19 000–22 000 K are determined from the Boltzmann-plot of 11 Ar ii spectral lines for which accurate A ki data are available from the literature. The transition probabilities of these 11 spectral lines were used for calculating new A ki-values. Electron densities (N e) of 3.5–9.0 × 1022 m−3 are determined by two-wavelength interferometry method. The measurements yield to a collection of 43 atomic transition probabilities of Ar ii lines in the spectral region of 294–386 nm, 11 of which are new, at least up to the authors knowledge, and 22 improved A ki-values for which the existing data in the literature have uncertainties around 50 per cent. Comparison with previous data shows how our measurements have good agreement with the most accurate A ki-values from the bibliography, whereas some of the values recommended by NIST present a significant disagreement.