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Go to top of ASD Help   Spectral Lines

The ASD database provides access to transition data for atoms and atomic ions. For more information on the Lines data accessible by the database consult the Introduction to and Contents of the ASD Database.

This section starts with the description of the input parameters of the Lines Search Form. For the description of the output, either in tabular or graphical form, see the Lines Output section.


Go to top of page  Lines Search Form

The ASD Lines Search Form, referred to as the "Lines Form," provides access to transition data for atoms and ions, either in tabular or graphical form. Tabular output is available for wavelengths, relative intensities, radiative transition probabilities and related quantities, as well as energy level classifications and bibliographic references. Graphical output is available in the forms of Grotrian diagrams, line identification plots, and Saha-LTE spectrum plots. For some spectra, there is also graphical information on dependences of certain line intensity ratios on electron density and/or temperature in the emitting plasma. This information can be useful for plasma diagnostics.

When loaded in the browser, the Lines Search Form displays only the Main search parameters block. At the bottom of this block, there are buttons "Reset Input," "Retrieve Data," "Show Graphical Options," and "Show Advanced Settings." When the "Show ..." buttons are clicked, the corresponding blocks of input options appear on the screen, and the buttons change their names to "Hide ..."

The Lines Form prompts the user for the following pieces of information: For the description of the output, see the Lines Output section.


Go to top of page  Main Search Parameters

At a minimum, the user must enter spectra of interest (e.g., H I) and then press the [Enter] key or click "Retrieve Data". This will result in a tabular output page with transition data. Alternatively, the user can click on the "Make Grotrian Diagram" button to produce an interactive graphical diagram. The Dynamic Plots require some additional settings, such as wavelength limits and units.

Go to top of page   Selecting Spectra for Line Searches

On the Lines Form, to specify an element, simply enter the element symbol (e.g., Fe). Element symbols and Roman numerals need not be capitalized. Multiple elements are separated by a semicolon. To indicate the spectrum of a given element, enter either a Roman numeral or an Arabic numeral after the element name. The Roman numerals must be separated from the element symbol by a space. (Note: Fe I = Fe0+, Fe II = Fe1+, etc.). Alternatively, the spectrum may be specified by the name of its isoelectronic sequence (e.g., Si Li-like = Si XII, Si Na-like = Si IV). The absence of a Roman or Arabic numeral or an isoelectronic sequence name after an element symbol indicates all stages of ionization. Spectra of the same element are separated by a comma, while spectra of different elements are separated by a semicolon. A range of spectra is indicated by using a hyphen between stages of ionization or between names of isoelectronic sequences.

If the user has not provided enough information to specify spectra, an error message will be displayed.

Examples of Spectral Notation (Case Insensitive)

Na I     Neutral sodium
na 0     Neutral sodium
Na I; Fe I     Neutral sodium and neutral iron
Fe I-III     Fe, ionization stages one, two, and three
Fe I-III,V     Fe, ionization stages one, two, three, and five
Fe     All ionization stages of iron
198Hg I     Neutral isotope 198 of mercury
C I; N II; O III     List of spectra specifying neutral carbon, nitrogen II, and oxygen III.
C-O C-like     List of carbon-like spectra of all elements between carbon and oxygen (produces the same results as the previous example).
C-O I-III     List of spectra of neutral, singly-ionized, and doubly-ionized elements between carbon and oxygen.
C-N I-II; Ne IV-V     List of spectra specifying C I, C II, N I, N II, Ne IV, and Ne V.
Mg He-like-Li-like; Al Li-like     List of spectra specifying Mg X, Mg XI, and Al XI.

Go to top of page   Lower and upper limits of the wavelength/wavenumber range

By default, the Search Form prompts the user to enter the lower and upper limits of line wavelengths in the units selected in the "Wavelength Units" menu. The user can select the "Wavenumber" option in the drop-down menu of the limit types. Then the expected input in the "Lower" and "Upper" input boxes is for the limiting wavenumbers in units of cm−1. The limits can be left blank if the Spectra box is non-blank and no Graphical Output Options are set.

Note that the wavelength units set in the drop-down menu in the Main Parameters section apply not only to the wavelength limits, but also to the output wavelengths. By default, the wavelengths are included in the output. The user can change the choice of the output columns in the output and set a number of other options (e.g., whether the wavelengths are in standard air or in vacuum) in the Advanced Settings section of the Search Form. These settings will be displayed if the user clicks on the "Show Advanced Settings" button.

For the description of the tabular output of the Lines Form, see the Output Line Tables section.

Go to top of page   Graphical Output Options

There are two sets of graphical output options in the Lines Search: To show these graphical options, the user must click on the "Show Graphical Options" button in the Main Parameters section. The contents and use of the graphical output are explained in the Graphical Output section.

Go to top of page  Dynamic Plot Options

These options allow graphical display of two types of dynamically created plots, i.e., line identification plots and Saha-LTE (local thermodynamic equilibrium) plasma emission plots. The plots are created as PDF files and require appropriate software (e.g., Adobe Acrobat Reader or xpdf) for graph display. See the Graphical Output section for the details on the output.

Go to top of page  Java Grotrian Diagrams

In order to have this feature operational, a user must have the most current Java Runtime Environment installed on his/her computer. This software is available for free download from this link.

As of 2017, most browsers stopped supporting Java applets, which are currently used in ASD to display Grotrian diagrams. One exception is Internet Explorer, which still displays them in the Microsoft Windows operating system. However, it requires the user to properly set the Java security options in the Windows Control Panel. Namely, the Security Level must be set to "High" and the website https://physics.nist.gov must be added to the exception list in the Security tab of the Java settings control. The ASD Team is planning to replace the Java applet implementation of the Grotrian diagrams with another graphical software. For now, to enable Grotrian Diagrams on your system, follow the steps below. You must use the Windows operating system.

  1. Uninstall all versions of Java you have on your computer.
  2. If Internet Explorer is not installed, or its version is <11, install the latest 32-bit version of Internet Explorer and open it.
  3. Go to java.com and install the latest Java version from the big red button they display at the top of the screen.
  4. Close all open windows of the Internet Explorer.
  5. Open the Java32 panel in the Windows Control panel.
  6. In the Java tab of the panel, verify that the installed version does not have "x64" anywhere in its description. If it does contain "x64," go back to the first step and try again.
  7. In the Security tab of Java32, set the Security Level to the lowest possible.
  8. Add https://physics.nist.gov to the exceptions list if it is not already there.
  9. Close the Internet Explorer and restart it.

The output content and features of interactive Grotrian diagrams are explained in the Plotting Java Grotrian diagrams section. The options of the input form are explained below.

Grotrian Diagram Options on the Lines Form page

Go to top of page   Advanced Settings

The options shown in this block of the Lines Form are divided into three groups:

Output Options

The following options apply to all lines and levels searches and are collectively referred to as output options.

The default is to display output in its entirety as an HTML formatted table. By default, the levels are displayed in cm−1.

For instructions on how to modify options associated with viewing data, refer to the section options for viewing data.

Go to top of page   Optional Search Criteria

The following search criteria may be specified:

Go to top of page   Additional Search Criteria

The following options apply to all line searches and are collectively referred to as additional search criteria options.

To change the default, the user simply needs to click on one of the radio buttons. The user will also need to check appropriate checkboxes if individual columns of wavelength information are desired:


Go to top of page  Lines Output

This section describes the output for different types of requests from the Lines Search Form:

Go to top of page  Output Line Tables

The output on the screen is HTML-formatted by default, but a significantly faster ASCII format may also be selected. The output will be even faster and more suitable for saving and viewing in other software, such as Excel or other spreadsheet viewers, if the No Javascript box is checked in the Optional Search Criteria section in the Advanced Settings block of the Lines Input Form. This box is automatically checked when the user selects the ASCII format. However, it can be unchecked if the output is intended solely for browsing purposes. The links to the online content of the bibliographic references are included in the output only if the No Javascript box is not checked.

Help popup windows

The output may contain some symbols or combinations thereof colored in red. This means that moving a mouse over such symbols would result in appearance of a small popup window showing some explanatory text provided the Javascript language is enabled in the browser options or preferences. Moving the mouse out would remove the popup window unless a user clicked on the red symbols. In that case, the popup window remains visible until the next mouse click on the same symbols. For the Ritz wavelengths, such popup windows appear also for the brown asterisk and pink plus symbols after the Ritz wavelengths (see below).

Go to top of page  Explanation of the Lines Tables

(By Column Heading)

Go to top of page  Ion

This column contains the spectrum name containing an element symbol and a Roman numeral denoting the spectrum number (I for neutral atom, II for singly ionized, etc.). This column appears only if multiple spectra have been specified in the Lines Form input.

Observed Wavelength, Ritz Wavelength, and Obs.-Ritz Wavelength

The Ritz wavelengths are the wavelengths derived from the lower and upper levels of the transitions. They are available only if both levels of the transition are known. If they are available, they usually are more accurate than the observed wavelengths, especially in the vacuum ultraviolet spectral region. The accuracy of the Ritz wavelengths depends on the quality of the energy level values. In some cases, the observed wavelength may be more accurate than the Ritz one, which is indicated by the number of given significant figures or by the uncertainties.

The user may choose to display both Ritz and observed wavelengths. The Obs-Ritz value may also be displayed. By default, wavelengths are given for vacuum wavelengths below 200 nm and above 2000 nm, with standard-air wavelengths in between. Conversion between the air and vacuum wavelengths used in ASD is explained here.

Go to top of page  Uncertainties of Observed and Ritz Wavelengths

Uncertainties of the data can be displayed, if they are available in ASD, when the corresponding box is checked in the input form (it is checked by default). If such information is not available, the implied uncertainty is defined by the number of significant figures given: it is generally between 2.5 and 25 units of the least significant figure. However, there are exceptions to this rule. In many cases, uncertainties of the relative positions of spectral lines can be measured more accurately than the wavelengths or wavenumbers. This may require additional significant figures in the wavelength values to avoid loss of accuracy. The quality of the Ritz wavelengths can also be assessed by estimating the average deviation "Obs.-Ritz" for the given spectral region. Sometimes, the uncertainties of both observed and Ritz wavelengths can be retrieved from the bibliographic references provided for each line or from the Primary Data Source references at the top of the output page. The user can always choose the best available wavelength from the ASD output.

All uncertainties given in ASD are meant to be on the level of one standard deviation.

Wavenumbers

There are two options for displaying wavenumbers in the output page: The Ritz wavenumbers in the ASD output are always calculated from the energy levels stored in ASD.

Go to top of page  Significant Figures

The number of significant figures in the ASD output values is determined by two considerations: About 90 % of data stored in ASD conforms to the rule of 25: the uncertainty is between 2.5 and 25 units of the least significant figure. Most of the exceptions are of the three origins: More details are given below for the number of significant figures given for observed and Ritz wavelength and wavenumbers and their uncertainties.

Go to top of page  Wavelengths

Precision of the given wavelengths is governed by their uncertainties, so we start with the determination of the uncertainty. If the uncertainty has been critically evaluated and is stored in ASD, we use this stored uncertainty value. Otherwise, we estimate the uncertainty of an observed wavelength as ten units of the least significant figure of the wavelength. For Ritz wavelengths with no critically evaluated uncertainty, we start with determining the uncertainties of the energy levels. If their critically evaluated values are available in ASD, we use them; otherwise, we estimate them as ten units of the least significant figure of the energy. Then we combine the level uncertainties in quadrature to obtain an estimated uncertainty of the Ritz wavenumber. This is used to derive the estimated uncertainty of the Ritz wavelength.

When there is no stored Ritz wavelength value in ASD, it is calculated online from the available energies of the lower and upper levels, and either an asterisk "*" or a plus "+" is appended to the Ritz wavelength value. The former simply indicates that this value was calculated online, while the latter points out that there are no critically evaluated values of the level uncertainties in ASD, and their estimation involves a number of trailing zeros in the stored energies, which were presumed insignificant. Therefore, the actual accuracy of the Ritz wavelengths followed by "+" may be higher. This involves only the energy values that do not contain a decimal point, usually in highly ionized atoms.

The subsequent procedure depends on the type of wavelength to be displayed: in vacuum or air.

Go to top of page  Wavenumbers

Observed wavenumbers stored in ASD are always shown as is, in units of cm−1. They may differ from the values derived from the observed wavelengths by a few units of the least significant figure due to rounding errors. If there is no stored value in ASD, but there is an observed wavelength, the observed wavenumber is calculated from the wavelength, and its value is rounded according to the rule of 25 using the stored or estimated uncertainty of the observed wavelength.

The Ritz wavenumbers are calculated from the energy levels stored in ASD. Their precision is entirely determined by their uncertainties, either stored in ASD (if they were critically evaluated) or estimated from the uncertainties of the energy levels by combining in quadrature the uncertainties of the lower and upper level of the transition. If there are no stored critically evaluated uncertainties of the levels, they are estimated as ten units of the least significant figure of the level value. Then the wavenumber value is rounded according to the rule of 25.

Definition of Ritz wavelength and wavenumber

"Ritz" wavenumbers are derived from level energies via the Ritz principle: the wavenumber σ of the emitted or absorbed photon is equal to the difference between the upper and lower energies Ek and Ei,

σ = EkEi.

The Ritz wavelength λ in vacuum is equal to the inverse of σ. If σ is in units of cm−1, and λ is in nanometers,

λvac [nm] = 107/(σ [cm−1]).

Wavelengths in air are decreased by the refractive index of air.

Rounding Rule of 25

A numerical value given in decimal representation is considered to be properly rounded if its uncertainty in the unit of the least significant figure is between 2.5 and 25.

If the rounding is too harsh, i.e., the uncertainty is smaller than 2.5 units of the least significant figure, the value of the uncertainty is statistical meaningless and the rounded value cannot be used in rigorous statistical analyses. See more about it in A. E. Kramida, Comput. Phys. Commun. 182, 419–434 (2011).

If the rounding is too mild, i.e., the uncertainty is greater than 2.5 units of the least significant figure, the precision of the value cannot be used to estimate the uncertainty. In cases when there are strong correlations between the given values, mild rounding may be needed to adequately represent the relative uncertainties of the presented data.

Go to top of page  Conversion between air and vacuum wavelengths

In vacuum, the wavelength λvac is directly determined by the wavenumber σ (see above). In air, it is decreased by the refractive index n:

λair  = λvac/n.

In ASD, the index of refraction of air is derived from the five-parameter formula given by E.R. Peck and K. Reeder, J. Opt. Soc. Am. 62, 958 (1972). These authors fitted data between 185 nm and 1700 nm. The conversion between air and vacuum wavelength entails an ambiguity near the boundary of the air region. For example, a wavelength of 200.0648 nm in vacuum corresponds to 200.0000 nm in "standard air" (i.e., 15 °C, 101 325 Pa pressure, with 0.033 % CO2). Conversely, an air wavelength of 199.9352 &nm corresponds to 200.0000 nm in vacuum. In this database, as the default, the following convention is adopted in terms of the energy difference or wavenumber, σ=Ek-Ei:

For σ ≥ 50,000 cm−1 → vacuum wavelengths,
For 5000 cm−1 < σ < 50,000 cm−1 → air wavelengths,
For σ ≤ 5000 cm−1 → vacuum wavelengths.

Thus, if the tabulated wavelength lies within 200 ± 0.0648 nm, one must check the energy difference to ascertain whether it is for vacuum or air.

The relative uncertainty δλ/λ of the formula of Peck & Reeder is 5×10−9 for wavelengths λ > 400 nm and increases according to the approximate formula

δλ/λ ≈ (0.35734 + 38.24/(λ − 180.29) + 0.000023λ)×10−8

for shorter wavelengths (λ is in nm). The maximum uncertainty is about 9×10−8 at 185 nm.

It should be noted that a number of other formulas for the refractive index of air exist in the literature. In particular, the formulas given by K. P. Birch and M. J. Downs, Metrologia 31, 315–316 (1994) have a five times lower uncertainty than the formula of Peck & Reeder, but only in a restricted wavelength range from 350 nm to 650 nm. Their validity in the extended wavelength region covered by the Peck & Reeder formula has never been verified.

Similarly, the "corrected" formulas given by P. E. Ciddor, Appl. Opt. 35, 1566–1573 (1996) are valid only in the wavelength range from 350 nm to 1200 nm and give increasingly large errors for shorter wavelengths: about −1.0×10−8 at 228 nm and −1.6×10−6 at 185 nm.

Go to top of page  Relative Intensity

Relative intensities are source dependent and typically are useful only as guidelines for low density sources.

These are values intended to represent the strengths of the lines of a spectrum as they would appear in emission. The values in the Database are taken from the cited publications. Usually, they are not normalized in any way. In some cases, the intensity values were derived from observed photometric signals. This would be true for spectra measured by Fourier transform spectroscopy or in special cases where spectra were recorded photometrically. However, in most cases the values represent blackening of photographic emulsions used to record an observed spectrum. These values can be semi-quantitative in that the transmission of the blackened emulsion was quantitatively measured and used to determine the intensity values. In other cases, the blackening was estimated visually and the estimates were used for the intensity values. Thus, the values can range from being approximately quantitative to only qualitative. Since the Database does not contain information on the origin of the relative intensities, the relative intensities should be considered as qualitative values that describe the appearance of a particular spectrum in emission.

The following points should be kept in mind when using the relative intensities:
  1. There is no common scale for relative intensities. The values in the database are taken from the values given by the authors of the cited publications. Since different authors use different scales, the relative intensities have meaning only within a given spectrum; that is, within the spectrum of a given element in a given stage of ionization.
  2. The relative intensities are most useful in comparing strengths of spectral lines that are not separated widely. This results from the fact that most relative intensities are not corrected for spectral sensitivity of the measuring instruments (spectrometers, photomultipliers, photographic emulsions).
  3. The relative intensities for a spectrum depend on the light source used for the excitation. These values can change from source to source, and this is another reason to regard the values as being only qualitative.

Descriptors to the relative intensities have the following meaning:

     *    Intensity is shared by several lines (typically, for multiply classified lines).
     :    Observed value given is actually the rounded Ritz value, e.g., Ar IV, λ = 443.40 Å.
     -    Somewhat lower intensity than the value given.
     a    Observed in absorption.
     b    Band head.
     bl   Blended with another line that may affect the wavelength and intensity.
     B    Line or feature having large width due to autoionization broadening.
     c    Complex line.
     d    Diffuse line.
     D    Double line.
     E    Broad due to overexposure in the quoted reference
     f    Forbidden line.
     g    Transition involving a level of the ground term.
     G    Line position roughly estimated.
     H    Very hazy line.
     h    Hazy line (same as "diffuse").
     hfs  Line has hyperfine structure.
     i    Identification uncertain.
     j    Wavelength smoothed along isoelectronic sequence.
     l    Shaded to longer wavelengths; NB: This may look like a "one" at the end
          of the number!
     m    Masked by another line (no wavelength measurement).
     p    Perturbed by a close line. Both wavelength and intensity may be affected.
     q    Asymmetric line.
     r    Easily reversed line.
     s    Shaded to shorter wavelengths.
     t    Tentatively classified line.
     u    Unresolved from a close line.
     w    Wide line.
     x    Extrapolated wavelength
Other characters occasionally appearing in the intensity column are explained in the quoted literature.

The difficulty of obtaining reliable relative intensities can be understood from the fact that in optically thin plasmas the intensity of a spectral line is proportional to:

Iik Proportional to NkAkihνik,

where Nk is the number of atoms in the upper level k (population of the upper level), Aki is the transition probability for transitions from upper level k to lower level i, and hνik is the photon energy (or the energy difference between the upper level and lower level). Although both Aki and νik are well defined quantities for each line of a given atom, the population values Nk depend on plasma conditions in a given light source, and they are thus different for different sources.

Go to top of page  Transition Strengths

Either transition probability "Aki" weighted transition probability "gkAki" (s−1 or 108 s−1), absorption oscillator strength or f value ("fik"), line strength "S", or "log(gf)" can be displayed. Note that fik, S, and log(gf) are not displayed by default. Also note that log(gf) is shorthand for log10(gi fik).

Aki represents the emission transition probability. In the following formulas, it is assumed to be in units of 108 sec−1.

fik is the absorption oscillator strength or f-value.
fik = Aki ·1.49919·10−16 gk/gi λ2, for all multipole types,
where λ is the wavelength in ångströms

log(gf) is the log10(gfik), where gi = 2Ji + 1.

S is the line strength. It is the electric dipole matrix element squared and is independent of the transition wavelength.

More details on these quantities can be found in this review.
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Go to top of page  Accuracy

An estimated accuracy is listed for each transition strength, indicated by a code letter as given in the table below:

AAA 0.3%
AA 1%
A+ 2%
A 3%
B+ 7%
B 10%
C+ 18%
C 25%
D+ 40%
D 50%
E > 50%.

The uncertainties are obtained from critical assessments, and in general, reflect estimates of predominantly systematic effects discussed in the NIST critical compilations, cited in the Bibliography. Accuracies are not available for values listed in the CRC handbook.

If the accuracy is followed by a prime (′), then a multiplet in the original compilation has been separated into its component lines and the transition probability was derived from the compiled value assuming spin-orbit coupling. This may decrease the listed accuracy, especially for weaker transitions.

**************************

Go to top of page  Conversion between transition probabilities and line strengths

Transition multipole: Multiply Aki by listed factor to get S:
E1   Electric dipole                 4.935525·10−19 gk λ3
M1   Magnetic dipole                 3.707342·10−14 gk λ3
E2   Electric quadrupole             8.928970·10−19 gk λ5
M2   Magnetic quadrupole             6.707037·10−14 gk λ5
E3   Electric octupole               3.180240·10−18 gk λ7
M3   Magnetic octupole                2.38885·10−13 gk λ7

where λ is the wavelength in angstroms and gk is the statistical weight of the upper level. The numerical factor for the electric quadrupole conversion from Aki to S follows a more modern convention than that used in the original publications, which will be used in future NIST publications.

Go to top of page  Ei-Ek

Lower level and upper level energies of the transition are displayed in the units specified. Note that, if the units other than cm−1 are requested in the Lines Search Form, uncertainties of the conversion factors are combined in quadrature with the uncertainties of the energy levels, which may result in loss of precision. However, the Ritz wavelengths and wavenumbers are always calculated from the stored energy levels in units of cm−1, so their precision is not affected.

Configurations

Configurations of the lower and upper levels are displayed. For ASCII output, periods are inserted in the configuration labels whenever necessary to avoid ambiguity due to the lack of superscripts, and angular brackets enclose J values of the parent term.

Terms 

Terms of the lower and upper levels are displayed. A superscript "°" in the HTML output or an asterisk in the ASCII output indicates odd parity.

J-values

The J-values represent the total electronic angular momentum of the lower and upper levels.

gi-gk

gi-gk represents statistical weight of the lower level (gi=2Ji+1) and statistical weight of the upper level (gk=2Jk+1).

Type

This filed is blank for allowed (electric-dipole, or E1) transitions, including the spin-changing (intercombination) transitions. Types of forbidden transitions are denoted as follows:

M1    - Magnetic dipole.
E2    - Electric quadrupole.
M2    - Magnetic quadrupole.
E3    - Electric octupole.
M3    - Magnetic octupole.
M1+E2 - Mixed magnetic dipole and electric quadrupole transition.
        The selection rules for these two types of transitions are the same, so
        both types of transitions can contribute to the observed intensity and
        radiative rate Aki. The line strength is undefined for such mixed transitions.
2P    - Two-photon transition.
HF    - Hyperfine-induced transition (may occur only in isotopes with a
        non-zero nuclear magnetic moment).
UT    - Forbidden transition of an unspecified type.

Transitions that are strongly forbidden in isolated atoms may be enabled by environmental effects such as external electric or magnetic fields. Such forbidden transitions would be denoted as type = UT in ASD.

The conversion formulas between transition probabilities and line strengths for different types of allowed and forbidden transitions are given here.

Go to top of page  TP Ref. and Line Ref.

There may be several reference codes separated by comma in each of these columns. If the "No Javascript" box was not checked in the Lines Search Form, each bibliographic code links to a popup window showing a bibliographic reference for transition probability or for the observed spectral line.

Plasma diagnostics data

For those lines that have diagnostic data in ASD, an additional column of the Lines Tabular Output contains links to detailed information about the line pairs whose relative intensities can be used to determine the plasma temperature and/or density. The diagnostic data include plots of intensity ratios versus electron temperature or density and specifications of the validity range of these plots.

Go to top of page  Graphical Output

 Dynamic Plots

Line Identification Plot

If the "Line Identification Plot" option has been selected on the Lines Form, two links will appear at the very bottom of the tabular output page, i.e., a link to a PDF file containing an image of the plot and a link to a new popup window displaying the wavelengths of the spectral lines shown on the PDF plot.

The Line Identification Plot is a stick plot showing the line positions for all chosen ions in the given wavelength range. It can be used to diagnose which ions produce spectral lines is an observed spectrum. For that, the image should be magnified or reduced to approximately the same wavelength scale as in the experimental spectrum. Then the patterns of intervals between the observed spectral lines could be matched with those in one or more of the ion spectra in the Line Identification Plot, which can help the user to identify the observed lines.

If there are too many lines in the chosen spectra, the user can use the "Relative intensity minimum" or other options in the Optional Search Criteria section in the Advanced Settings block of the Lines Input Form to reduce the number of shown lines.

Saha-LTE Spectrum Plots

The Saha-LTE plot shows the distribution of calculated intensities in the plasma emission spectrum for the chosen ions within the selected wavelength range.

If the "Saha-LTE Plot" option has been selected on the Lines Form, two or more links will appear at the very bottom of the tabular output page. One of them is a link to a PDF file containing an image of the plot. One of the other links with text "Relative Line Intensities" is to a new popup window displaying the wavelengths of the spectral lines shown on the PDF plot and their relative intensities. If the user requested a Doppler-broadened spectrum (by checking the corresponding box in the Lines Form), there will be two additional links, one to table of calculated intensities of each ion in the Doppler-broadened spectrum, and one to a table showing the distribution of intensities in the total spectrum (sum of contributions from each ion). Both these tables are two-column plane fixed-column-width ASCII files with the first column having the wavelength grid points and the second column having relative intensities in arbitrary units. These tables can be used to plot the spectra with other software.

The header of the plot shown in the PDF file shows the user-defined parameters: composition of the element mixture in the plasma, electron temperature and density, as well as the total number of lines in the synthetic spectrum. If a Doppler-broadened spectrum was requested, the header also shows the ion temperature used to calculate the Doppler broadening. It may be greater than the Ion Temperature specified by the user in the Lines Input Form, if the number of required points in the grid was too large for the given selection of spectral lines. In such cases, to display narrower lines (corresponding to a lower ion temperature), the user needs to reduce the selected wavelength range, reduce the number of requested spectra, or use some line-filtering options in the Optional Search Criteria section in the Advanced Settings block of the Lines Input Form.

If higher resolution (narrower lines) is needed, and only neutral, singly-ionized, or doubly-ionized atoms are involved, consider using the LIBS Interface of ASD. Although this interface does not allow drawing spectra for a particular ionization stage, its plots can be calculated on the user's computer with much higher resolution, and they have flexible interactive features.

Go to top of page  Plotting Java Grotrian diagrams

Working with the Grotrian diagram plot

Basically, only a computer mouse and a space bar are used for interaction with this plot.


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