ИСТИНА

Parameters of Stark broadening are of interest for plasma diagnostics since they can be fruitful for non-LTE plasmas. Not surprisingly, it is widely used to characterize the glow discharge, the discharge in a hollow cathode, high-density star plasma and other plasma objects. Unfortunately, there is a lack of the theoretical data on Stark broadening for several elements like as atomic manganese. Recent experimental attempts to estimate Stark widths of Mn I lines belonging to multiplets z6P°→a6S and z6D°→a6D resulted in a discrepancy. For example, Stark width for line of Mn I 403.07 nm rescaled to Ne=1017 cm-3 was estimated by Bredice et al1 (T=104 K) as 0.005 nm vs. 0.022 nm from Srećković et al2 (T=4.7×104 K). Since self-absorption is the main source of systematic error in Stark width measurements, which causes an over-estimation of the line widths3, in the present work, we used Al alloys containing 0.03% wt. of manganese to reduce a self-absorption for these Mn I lines. A long plasma was produced by a cylindrical lens in order to increase a collection of plasma radiation. Then it was projected on a slit of 0.32 m Czerny-Turner spectrograph (instrumental width 0.017 nm at 404 nm). The ratio of resonance line intensities in manganese triplet at 403 nm (1:0.75:0.5) corresponded to the ratio of oscillator strengths. Taking into account small content of manganese and the ratio of line intensities, we suggested that there was no self- absorption of these lines according to Konjevic4. Plasma temperature was low as usual LIBS plasma (5000 K at 1.5 μs), and the line Al II 281.62 nm fully disappeared by 1 μs. Therefore, we have used known Stark widths and shifts for lines of Mg I 516.73 nm and Mg I 517.27 nm to study the evolution of electron density. It was changed in a range of 5-20×1016 cm-3. Despite a relatively low temperature we have not observed a distortion of line Mn I 403.07 nm due to a hyperfine structure as it was calculated by Srećković et al2. Stark widths for both resonance lines of Mn I (z6P°→a6S) and lines belonging to z6D°→a6D were about 0.010 nm at Ne=1017 cm-3. Possible reasons for discrepancy of our results with other experimental results are thoroughly discussed. References: 1 F. Bredice, F.O. Borges, H. Sobral, M. Villagran-Muniz, H.O. Di Rocco, G. Cristoforetti, S. Legnaioli, V. 2 Palleschi, A. Salvetti, and E. Tognoni, Spectrochim. Acta. Part B 62 (2007) 1237-1245. 2 A. Srećković, Z. Nikolić, S. Bukvić, and S. Djeniže, J. Quant. Spectrosc. Radiat. Transfer 105 (2007) 536-541. 3 C. Aragón, and J.A. Aguilera, Spectrochim. Acta Part B 63 (2008) 893–916. 4 N. Konjevic, Physics Reports 316 (1999) 339-401.