ION BROADENING OF SODIUM nS - 3P TRANSITIONS Z. Miokovic 1 and D. Veza

1. ION BROADENING OF SODIUM nS - 3P TRANSITIONS Z. Miokovic1and D. Veza Physics Department, Faculty of Science, Uni-Zagreb, Bijenicka 32, HR-10002 Zagreb, Croatia (veza@phy.hr) 1Faculty of Electrical Engineering, Uni-Osijek, K. Trpimira 2B, 31000 Osijek, Croatia (zeljka@etfos.hr) • MOTIVATION • Better understanding of the physics and chemistry of high-pressure discharges (sodium-mercury /cadmium and metal-halide discharges) • Importance of atomic plasma parameters for modeling high-pressure discharges and optimization of metal-halide and alkali lamps • The line shift and the line broadening of nD – 3P (n > 4) series and nS – 3P (n = 5, 6, 7) series are rarely investigated • To find out mechanisms leading to the formation of nS-3P (n = 5, 6, 7) sodium atomic lines and to determine the corresponding interaction constants • Sodium nS-3P (n = 5, 6, 7) atomic lines emitted from high-pressure sodium discharges [1, 2, 3] show a systematic red asymmetry EXPERIMENT Fig. 3. The 52D3/2, 5/2 32P1/2;3/2 atomic lines measured from the HP 400W Na-Cd discharge at the current of 3.4 A (hollow circles). The solid red line represents the best fit of Lorentzian profiles to the experimental data measured from the HP discharge. The lower part shows the same atomic lines measured from the low-pressure sodium spectral lamp (reference source, unshifted lines). Fig.1. Experimental arrangement: LPL- low pressure lamp; HPL-high pressure lamp; R- folding mirror; L-lens; F-cut of filter; M-monochromator; PMT-photomultiplier; A/D-analog-to-digital converter; PC-personal computer. Fig. 2. The external- or the line triggering for the time resolved measurements is used, provided by boxcar averager. All measurements were performed at the maximum value of the AC driving current. RESULTS Fig. 4.: The comparison of our measured Stark shift de of sodium 7 2S1/2 - 3 2P1/2,3/2 line at 475 nm, radiated from HP 400 W Na-Cd () and Na - Hg () discharges, and Stark (electron-impact) half widths we determined by fitting the simulated line shapes calculated within Bartels’ method with calculations by Griem (1964., full line) and Dimitrijevic et. al (1985., dotted line). The 7 2S1/2 - 3 2P1/2,3/2 line was used as the calibrant line, used to deliver values of Ne at different currents through the discharges. Fig. 5.: The 72S1/2 32P1/2;3/2 atomic line measured from the 400W Na-Cd discharge at the current of 4.0 A (circles). The theoretical profiles (full and dotted lines, representing the best fit to the experimental data), calculated using the Bartels’ method [7] with the following plasma parameters: NNa = 21023 m-3, NCd = 201023 m-3, Ne = 7.581021 m-3 , de = 0.085 nm, di = 0.0121 nm, we = 0.080 nm, wi = 0.0106 nm and Te = 3850 K. The dotted line represents the analytical line profile calculated according to Stormberg [4]. This calculation takes into account the line broadening by electrons and the van der Waals broadening by Cd (or Hg) atoms. The full line represents a profile calculated by numerical convolution [5] of the reduced Stark profile accounting for the quasistatic approximation for ions and the impact approximation for electrons, and also the van der Waals broadening by Cd (or Hg) atoms. The lower part shows the difference between experimental and theoretical profiles. Table 1.: The electron broadening caused shift and width data (de ,we) and ion broadening data (di , wi) of the sodium n2S1/2 32P1/2;3/2 (n=5, 6, 7) atomic lines radiated from high-pressure Na-Cd discharge are tabulated for given electron density and temperatures. The Stark-broadened line-width (1/2 )S and line-shift (1/2)S are given by [6] (1/2)S = [ 1+1.75 A (1 - 0.75 r) ] w , (1/2)S = [ d/w + 2 A (1 - 0.75 r) ] w , where is w = 2 we Ne / 1016. The appropriate values of the quasi-static ion broadening parameter A and the Debye shielding parameter r : 0.086 < A < 0.151 , 0.626 < r < 0.65. • CONCLUSIONS • We measured the Stark-shift, -width and shape of neutral sodium spectral lines corresponding to the n 2S1/2 - 3 2P1/2, 3/2 (n = 5, 6, 7) transitions, measuring the side-on emission from a high-presssure sodium discharge • Electron density determined measuring the shift of the sodium 72S1/2 32P1/2;3/2 spectral line • Electron temperature determined by Bartels’ method (fitting the calculated to the experimentally measured line shapes) • The dominant shift and broadening mechanism is the Stark broadening • Line-shifts and widths of the sodium nS - 3P (n=5, 6, 7) transitions show a linear dependence on the electron density • The red asymmetry of sodium atomic lines can be explained by a combined effect of ion broadening (the dominant one) and foreign gas (Cd or Hg) broadening. • References • [1] Z. Miokovic, D. Balkovic, D. Veza, Proceedings of the 34th EGAS, • pp P2: 58-59. (Sofia, 9-12 July 2002). • [2] Z. Miokovic,and D. Veza, FIZIKA A10, 129 (2001). • [3] Z. Miokovic, D. Balkovic, D. Veza, submitted for publication. • [4] H. P. Stormberg, J. Appl. Phys. 51, 1963 (1980). • [5] W. H. Press, S. A. Teukolsky, W. T. Vetterling, Numerical Recipes in C, Cambridge UP, New York (1992). • [6] M. S. Dimitrijevic, S. Sahal-Bréchot, J. Quant. Rad. Trans. , 34, No. 2, 149 (1985) • [7] H. R. Griem, Plasma Spectroscopy, McGraw-Hill, New York (1964). • [8] H. Bartels, Z. Phys. 128, 546 (1950).