Effects of Ion Motion on Hydrogen Stark Profiles

Abstract

The influence of ion motion on Stark broadened hydrogen lines is studied using the Method of Model Microfields which allows a uniform unified treatment of electrons and ions. Contrary to former theoretical investigations, strong effects are found in the line centres of L-a, H-a, and H-ß which agree well with recent experimental findings, especially those of Wiese, Kelleher, and Helbig. E ffects o f I o n M o tio n o n H y d r o g e n S ta rk P ro files For the Stark broadening of hydrogen lines the unified theory developed by Voslamber 1 and Smith et al.2 provides a refined description of line profiles including the transition region from the "static" wing to the "impact" centre. Evaluating the results of the unified theory, Vidal, Cooper, and Smith3 (VCS) have compiled extensive tables of Stark pro files of low Lyman and Balmer lines which greatly facilitate the comparison to experimental results. A detailed experimental investigation of the Stark broadening of Balmer lines has been carried through by Wiese, Kelleher, and Paquette 4 (WKP) who give a short account as well of former measurements which have been done in the same range of plasma densities and temperatures (typical values are Ne = 1017 cm-3, T = 104 K ). As a general result, good agreement between theory and experiment is found in the line wings but the measured profiles exhibit much less structure in their central portions than those of VCS. A similar finding has been reported 5 for low electron densities, too, and the conclusion seems to be inevitable that not all the approxima tions used in the VCS calculations work as good in ithe line centre as has been estimated.Possible candidates are especially the neglect of time ordering in the evaluation of the effects of radiator-perturber collisions, and the assumption of a static ion microfield. The first of these is not a constituent part of the unified theory but may be removed at the expenditure of greater calculational efforts. Corresponding results of Roszman6 indicate that the inclusion of time ordering improves the agreement of experiment and theory, but certainly is not sufficient to remove the discrepancies. This has been made most obvious by a recent experiment Reprint requests to Dr. J. Seidel, Institut für Theoretische Physik der Universität Düsseldorf, Universitätsstraße 1, D-4000 Düsseldorf.of Grützmacher and Wende 7 who succeeded to mea sure the line centre of L-a for the first time. While they report a half width of more than twice the theoretical value, its increase by the consideration of time ordering in the VCS calculations 8 amounts to only 14%. This points out to an influence of ion dynamics much stronger than has been expected, and indeed there is convincing experimental support of this conjecture: Precision measurements of Wiese, Kelleher, and Helbig9 (WKH) revealed distinctly different line centres for various values of the ra diating atom-perturbing ion reduced mass /u. More over, these authors found that an extrapolation to jU = oc, based upon the assumption of a linear de pe...

Hydrogen spectral lines with the inclusion of dense-plasma effects

“…In fact, their incorporation results in an increase of the L half-width by a factor of about 2 and, furthermore, leads to a remarkable reduction of the dip in the center of L& [37][38][39][40], while for H the half-width TABLE I. Electron shift of the H line at -' of the intensity maximum (n, =10' cm, T=12000 K). decreases only by about 15% [34,41] for the discussed plasma conditions.…”

Spectral-Kinetic Coupling and Effect of Microfield Rotation on Stark Broadening in Plasmas

“…Within the assumptions of ST the plasma ions are considered as static [17,18,21], and hence the resultant Stark profiles are called static or quasistatic. We now consider the ion dynamics effects, i.e., the deviations from the static Stark profiles due to the thermal motion (see, for example, [7][8][9]12,17,18,20,21,[23][24][25][26][27][28][29][30][31][32][33][34][35][36][74][75][76]). If these deviations are small enough (called in earlier works "thermal corrections" The basic idea of Markov construction of these joint distributions is that , F F    and F   are stochastic independent variables, formed by summation of electric fields or its derivatives over all individual ions of the medium [1,5,6].…”

“…Thus, simultaneously with the computer simulations the development of model approaches, that accounted for the ion dynamical effects in an approximate manner, were carried on independently [32][33][34][35][36][37]39,41,46,49,53,54,56,[59][60][61][62][63][64][68][69][70][71][72][73][74][75][76]. The first such model (actually, predating computer simulations) was MMM [14,15,28,29,52], later followed by various applications of the BID [37,71] and Frequency Fluctuation Model (FFM) [46,56,66] methods. Notably, neither of these models explicitly accounts for the effects of microfield rotation [24,25,30,33,53].…”

“…The necessity of this discussion arose when it was recently shown that existing approaches to accounting for ion dynamics give results that differ from one another [74][75][76]. This inspired attempts to describe ion dynamics effects in terms of physical mechanisms, instead of practically tacit conventional numerical comparison of complicated simulations that began with the first works done using the Model Microfield Method (MMM) in the 1970s [14,15,28,29]. The basics of the theory of thermal corrections for Stark profiles along with the results of [7][8][9]12,[23][24][25] are given in Section 3.…”

Spectral Line Shapes of He I Line 3889 Å

“…Several theoretical approaches have been applied to calculate Stark broadening, such as the well known semiclassical approximation the standard theory (ST) by Griem [1], or the quantum statistical approach of many-particle theory [2], where the motion of ion perturber is neglected during the inverse halfwidth of the line. Furthermore, the model microfield method (MMM) [3][4][5][6], the frequency fluctuation method (FFM) [7] or computer simulations [8][9][10][11] are used for calculating the line broadening including ion-dynamics effects, which lead to further broadening of the line shapes.…”