The impact theory of spectral line shapes: a paradigm shift

2013 ◽  
Vol 91 (11) ◽  
pp. 879-895 ◽  
Author(s):  
A.D. May ◽  
W.-K. Liu ◽  
F.R.W. McCourt ◽  
R. Ciuryło ◽  
J. Sanchez-Fortún Stoker ◽  
...  
Keyword(s):  
Spectral Line ◽  
Line Shape ◽  
Paradigm Shift ◽  
Wigner Distribution ◽  
Kinetic Equations ◽  
Line Profiles ◽  
Line Shapes ◽  
Experimental Line ◽  
Impact Theory ◽  
The Impact

An overview of the binary collision impact theory of spectral line shapes has been given to provide a unified statistical mechanical approach to line-shape theory, laser theory, nonlinear optics, and transport phenomena in dilute gases. The computation of spectral line profiles corresponding to those obtained from ultra-high-resolution spectral line-shape measurements requires numerical ab initio calculation of scattering amplitudes directly from the underlying dynamics of collisions between radiatively active molecules and their perturbers. The Wigner distribution function–density matrix is utilized to describe the kinetic theory of spectral line shapes and to discuss the various collisional processes that contribute to the kernel of kinetic equations. The influence of features of the potential energy surface on spectral parameters is also discussed, and the importance of comparing experimental line profiles directly with numerically computed line shapes obtained from reliable interaction potentials is emphasized. This contrasts sharply with the universal practice of comparing experimental line widths and shifts using some average or approximate theoretical scattering cross-sections and it contrasts sharply with fitting experimental profiles to some convenient analytical line-shape model; hence the phrase “a paradigm shift” in the title of this work.

Collisional Narrowing and the Foreign Gas Broadening of Spectral Line Shapes

1972 ◽  
Vol 50 (22) ◽  
pp. 2792-2800 ◽  
Author(s):  
H. R. Zaidi
Keyword(s):  
Spectral Line ◽  
Line Shape ◽  
Point Of View ◽  
Many Body ◽  
Spectral Line Shape ◽  
Many Body Theory ◽  
Line Shapes ◽  
The Many ◽  
The Impact ◽  
Body Theory

The problem of collisional narrowing and broadening of spectral line shape in a gas is considered from the point of view of propagator technique of the many body theory. The case in which the radiator and perturbers are of different species is considered in this paper. In the impact limit, the propagator equations reduce to a form which is a generalization of the classical equations used in the previous theories. The line shapes resulting from the two approaches are compared and possible generalizations are discussed.

scholarly journals From the Vector to Scalar Perturbations Addition in the Stark Broadening Theory of Spectral Lines

Universe ◽  
2021 ◽  
Vol 7 (6) ◽  
pp. 176
Author(s):  
Valery Astapenko ◽  
Andrei Letunov ◽  
Valery Lisitsa
Keyword(s):  
Spectral Line ◽  
Stark Effect ◽  
Coulomb Field ◽  
Spectral Lines ◽  
Alternative Methods ◽  
Scalar Perturbation ◽  
Numerical Comparison ◽  
Line Shapes ◽  
Stark Effects ◽  
The Impact

The effect of plasma Coulomb microfied dynamics on spectral line shapes is under consideration. The analytical solution of the problem is unachievable with famous Chandrasekhar–Von-Neumann results up to the present time. The alternative methods are connected with modeling of a real ion Coulomb field dynamics by approximate models. One of the most accurate theories of ions dynamics effect on line shapes in plasmas is the Frequency Fluctuation Model (FFM) tested by the comparison with plasma microfield numerical simulations. The goal of the present paper is to make a detailed comparison of the FFM results with analytical ones for the linear and quadratic Stark effects in different limiting cases. The main problem is connected with perturbation additions laws known to be vector for small particle velocities (static line shapes) and scalar for large velocities (the impact limit). The general solutions for line shapes known in the frame of scalar perturbation additions are used to test the FFM procedure. The difference between “scalar” and “vector” models is demonstrated both for linear and quadratic Stark effects. It is shown that correct transition from static to impact limits for linear Stark-effect needs in account of the dependence of electric field jumping frequency in FFM on the field strengths. However, the constant jumping frequency is quite satisfactory for description of the quadratic Stark-effect. The detailed numerical comparison for spectral line shapes in the frame of both scalar and vector perturbation additions with and without jumping frequency field dependence for the linear and quadratic Stark effects is presented.

THE SHAPES OF PHOTOELECTRON SATELLITE SPECTRA

2002 ◽  
Vol 09 (02) ◽  
pp. 1209-1212 ◽  
Author(s):  
V. G. YARZHEMSKY ◽  
V. I. NEFEDOV ◽  
M. YA. AMUSIA ◽  
L. V. CHERNYSHEVA
Keyword(s):  
Line Shape ◽  
Shape Parameters ◽  
Line Shapes ◽  
Peak Structure ◽  
Experimental Line

Line shapes of photoionization satellites are theoretically investigated. Calculations were carried out for the satellite states 1s2s(3S)3s(2S) and 3s3p5(1P)4s(2P) of Ne 1s and Ar 3p vacancies, respectively, created in photoionization. Theory excellently reproduces experimental line shape parameters of the first satellite and predicts the two-peak structure of the second.

Complete Line Shape for the Impact, Static, and the Intermediate Regions

1975 ◽  
Vol 53 (1) ◽  
pp. 84-92 ◽  
Author(s):  
R. P. Srivastava ◽  
H. R. Zaidi
Keyword(s):  
Density Dependence ◽  
Line Width ◽  
Line Shape ◽  
Translational Motion ◽  
Excited Level ◽  
Dipole Interaction ◽  
Line Shapes ◽  
Classical Path ◽  
The Impact ◽  
Resonance Broadening

Line shapes are calculated for the resonance broadening of an excited level through the dipole–dipole interaction. The calculations are based on two main approximations: (1) two body collisions and (2) straight classical path for the translational motion. The results are valid over the complete region extending from the impact to the static regimes. It is shown that, under suitable conditions, the incomplete collisions can give rise to (a) a splitting of the line at the center and (b) nonlinear density dependence of the line width.

scholarly journals Fast Rotating Stars: Effect of the Aspect Angle on Line Profiles

2004 ◽  
Vol 215 ◽  
pp. 23-24 ◽  
Author(s):  
Y. Frémat ◽  
J. Zorec ◽  
A. M. Hubert ◽  
M. Floquet ◽  
N. Leister ◽  
...  
Keyword(s):  
Spectral Line ◽  
Parameter Determination ◽  
Fundamental Parameter ◽  
Line Profiles ◽  
Rotating Stars ◽  
Chemical Abundances ◽  
Aspect Angle ◽  
Line Shapes ◽  
Density Distributions ◽  
On Line

Fast rotation is expected to flatten the star and to produce non uniform temperature and density distributions (i.e. gravitational darkening). While the flattening mostly increases the absolute flux level of the energy distribution, gravitational darkening makes an equator-on star apparently cooler than a star seen through the pole. Both effects (Collins et al. 1991) influence the colours and the location of the star in the HR diagram but also, in a more subtle way, its spectral line profiles. More particularly, in early B type stars, gravitational darkening tends to privilege at the poles the formation of the ions with the highest ionization potentials and directly affects line formation. Consequently, most spectral line shapes - and especially the weakest ones - become aspect angle dependent which in several cases may play a role in the fundamental parameter determination procedures or even in the determination of stellar chemical abundances.

scholarly journals The Coulomb Symmetry and a Universal Representation of Rydberg Spectral Line Shapes in Magnetized Plasmas

Symmetry ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 1922
Author(s):  
Andrei Letunov ◽  
Valery Lisitsa
Keyword(s):  
Spectral Line ◽  
Line Shape ◽  
Coulomb Field ◽  
Analytical Description ◽  
New Method ◽  
Magnetized Plasmas ◽  
Balmer Series ◽  
Line Shapes ◽  
Symmetry Properties ◽  
Atomic States

A new method of line shape calculations of hydrogen-like atoms in magnetized plasmas is presented. This algorithm makes it possible to solve two fundamental problems in the broadening theory: the analytical description of the radiation transition array between excited atomic states and an account of a thermal ion motion effect on the line shapes formation. The solution to the first problem is based on the semiclassical approach to dipole matrix elements calculations and the usage of the specific symmetry properties of the Coulomb field. The second one is considered in terms of the kinetic treatment of the frequency fluctuation model (FFM). As the result, one has a universal description of line shapes under the action of the dynamic of ion’s microfield. The final line shape is obtained by the convolution of the ionic line shape with the Voigt electron Doppler profile. The method is applicable formally for large values of principal quantum numbers. However, the efficiency of the results is demonstrated even for well known first members of the hydrogen Balmer series Dα and Dβ lines. The comparison of obtained results with accurate quantum calculations is presented. The new method may be of interest for investigations of spectral line shapes of hydrogen-like ions presented in different kinds of hot ionized environments with the presence of a magnetic field, including So L and divertor tokamak plasmas.

scholarly journals Hydrogen Line Shapes in Plasmas with Large Magnetic Fields

Atoms ◽  
2020 ◽  
Vol 8 (4) ◽  
pp. 74
Author(s):  
Joël Rosato
Keyword(s):  
Plasma Diagnostics ◽  
Line Shape ◽  
Zeeman Effect ◽  
Line Profiles ◽  
Stark Broadening ◽  
Hydrogen Line ◽  
Line Shapes ◽  
Code Comparison ◽  
Computer Simulation Technique ◽  
Quadratic Zeeman Effect

We report on hydrogen line shape calculations in the presence of an external magnetic field, at conditions such that the quadratic Zeeman effect is important. The latter is described through a term proportional to B2 in the Hamiltonian, accounting for atomic diamagnetism. It provides a shift and an asymmetry on Lorentz triplets, and it leads to the occurrence of forbidden components. Motivated by investigations performed at the fifth edition of the Spectral Line Shape in Plasmas (SLSP5) code comparison workshop, we perform new calculations of hydrogen Lyman line profiles. Field values representative of magnetized white dwarf atmosphere conditions are taken. The calculations are done using a computer simulation technique, designed for Stark broadening modeling. A discussion of the results is done in the framework of plasma diagnostics.

scholarly journals Self-Absorption Analysis of Silver Resonance Lines in Nano-Material Laser Produced Plasma

2018 ◽  
Author(s):  
Ashraf M. El Sherbini ◽  
Mohamed A. Hagras ◽  
Mohamed R. Rizk ◽  
El-Sayed A. El Badawy ◽  
Christian G. Parigger
Keyword(s):  
Spectral Line ◽  
Line Shape ◽  
Absorption Analysis ◽  
Shape Distortion ◽  
Laser Device ◽  
Balmer Series ◽  
Line Shapes ◽  
Nano Material ◽  
Temperature And Pressure ◽  
532 Nm

The resonance spectra of neutral silver indicate self-absorption for the studied Ag I lines at the wavelengths of 327.9 nm and 338.2 nm. The center dip is associated with self-reversal due to self-absorption in the plasma. The Q-switched radiation of 355 nm, 532 nm, or 1064 nm from a Nd:YAG laser device generates the plasma at the surface of silver nano-material targets, with experiments conducted in standard ambient temperature and pressure laboratory air. Procedures for recovery of the spectral line shapes confirm that over and above the effects of self-reversal, line shape distortion are important in the analysis. The work discusses parameters describing self-absorption when using fluence levels of 2 to 33 J/cm2 to generate the plasma. Furthermore, subsidiary calibration efforts that utilize the hydrogen alpha line of the Balmer series show that the Ag I lines at 827.35 nm and 768.7 nm are optically thin.

scholarly journals The Frequency Fluctuation Model for the van der Waals Broadening

2021 ◽  
Author(s):  
Andrei Letunov ◽  
Valery Lisitsa ◽  
Valery Astapenko
Keyword(s):  
Experimental Data ◽  
Spectral Line ◽  
Line Shape ◽  
Frequency Fluctuation ◽  
Neutral Particles ◽  
Line Shapes ◽  
First Time ◽  
Analytical Expressions ◽  
Fluctuation Model ◽  
Good Agreement

The effect of atomic and molecular microfied dynamics on spectral line shapes is under consideration. This problem is treated in the framework of the Frequency Fluctuation Model (FFM). For the first time the FFM is tested for the broadening of a spectral line by neutral particles. The usage of the FFM allows one to derive simple analytical expressions and perform fast calculations of the intensity profile. The obtained results was compared with Chen and Takeo theory (CT), which is in a good agreement with experimental data. It was demonstrated that for moderate values of temperature and density the FFM successfully describes the effect of the microfield dynamics on a spectral line shape.

scholarly journals Broadening of the Neutral Helium 492 nm Line in a Corona Discharge: Code Comparisons and Data Fitting

2018 ◽  
Author(s):  
Roshin Raj Sheeba ◽  
Mohammed Koubiti ◽  
Nelly Bonifaci ◽  
Franck Gilleron ◽  
Jean-Christophe Pain ◽  
...  
Keyword(s):  
Emission Line ◽  
Corona Discharge ◽  
Line Shape ◽  
Diagnostic Technique ◽  
Parameter Determination ◽  
Line Profiles ◽  
Plasma Parameters ◽  
Line Shapes ◽  
Physical Effects

Passive plasma spectroscopy is a well-established non-intrusive diagnostic technique. Depending on the emitter and its environment which determine the dominant interactions and effects governing emission line shapes, passive spectroscopy allows the determination of electron densities, emitter and perturber temperatures as well as other quantities like abundances. However, using spectroscopy needs appropriate line shape codes retaining all the physical effects governing the emission line profiles. This requires for line shape code developers to continuously correct or improve them to increase their accuracy when applied for diagnostics. This is exactly the aim expected from code-code and code-data comparisons. In this context, the He I 492 nm emitted in a helium corona discharge at room temperature represents an ideal case since its profile results from several broadening mechanisms: Stark, Doppler, resonance and van der Waals. The importance of each broadening mechanism depends on the plasma parameters. Here the profiles of the He I 492 nm in a helium plasma computed by various codes are compared for a selected set of plasma parameters. In addition, preliminary results related to plasma parameter determination using experimental spectra from a helium corona discharge at low pressure 1- 2 bars, are presented.

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