Intensity ratios of H lines. Departures from the ideal conditions in the range of LIBS experiments.

CRUZADO, A.; DI ROCCO, H.

APPLIED SPECTROSCOPY

University of Hamburg

Lugar: Alemania; Año: 2007 vol. 61 p. 1084 - 1092

0003-7028

In the present paper we analyze the behavior of H line intensity ratios with electron density and electron temperature in intermediate-densityplasmas. We analyze the influence on the line intensity ratios of (1) the departures from local thermodynamic equilibrium (LTE) of the level population ratios, (2) the plasma opacity, and (3) the lowering of the ionization potential. We look, particularly, at the lines Ha, Hb, Hc, and Hd and the energy levels involved in the corresponding atomic transitions for their use as diagnostics in laser-induced breakdown spectroscopy (LIBS) experiments. One important conclusion is that, for typical values of the plasma dimension and the electron temperature taking place in LIBS, i.e., L ¼ 1 mm and Te ¼ 10 000 K, respectively, the intensity ratios Hb/Ha, Hc/ Ha, and Hd/Ha depart from the ideal values by less than 10% in the interval 0.6531014 part/cm3 NHI 3.631017 part/cm3, which means 1 31014 part/cm3 Ne 131016 part/cm3 for a gas of pure hydrogen. For higher densities, the departures from ideal conditions increase very quickly due to opacity effects. Ha, Hb, Hc, and Hd and the energy levels involved in the corresponding atomic transitions for their use as diagnostics in laser-induced breakdown spectroscopy (LIBS) experiments. One important conclusion is that, for typical values of the plasma dimension and the electron temperature taking place in LIBS, i.e., L ¼ 1 mm and Te ¼ 10 000 K, respectively, the intensity ratios Hb/Ha, Hc/ Ha, and Hd/Ha depart from the ideal values by less than 10% in the interval 0.6531014 part/cm3 NHI 3.631017 part/cm3, which means 1 31014 part/cm3 Ne 131016 part/cm3 for a gas of pure hydrogen. For higher densities, the departures from ideal conditions increase very quickly due to opacity effects. Index Headings: Laser-induced breakdown spectroscopy; LIBS; Hydrogen; Plasma spectroscopy; Plasma diagnostics.