Online: March 1999 - Last update: September 2005 |
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Spectral Lines
Lines Search FormFor searches, a variety of output options, optional search criteria, and additional search criteria are available.
Lines searches are either wavelength ordered or multiplet ordered.
Dynamic Plots
This option allows 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 Output Section for the details on the output.
Java Grotrian Diagrams
The following options apply to all lines and levels searches and are collectively referred to as output options.
Multiplets are transitions that share the same term and configuration. Multiplets have been ordered in the transition probability compilations according to energies and g values of the lower and upper levels, and have been assigned arbitrary multiplet numbers that reflect this order.
To view multiplet ordered data, the user must select the "multiplet ordering" radio box.
In some cases, a multiplet is missing from the numbered list. In general, this is because some property of a compiled wavelength or level involved is not consistent with other more recent compilations, such as the NIST energy level data. Note that with multiplet ordering, only those lines with transition probability values will be displayed. Moreover, the output will always be for vacuum wavelengths.
Only the lines with energy level classification are displayed in the multiplet-ordered output, and therefore the total number of lines shown at the top of the page may be different for wavelength and multiplet orderings.
The default is to display output in its entirety as an HTML formatted table. By default, 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.
The following search criteria may be specified:
There are numerous options that apply for lines searches. The following options apply to all lines searches and are collectively referred to as additional search criteria options.
The default is to display all lines of data meeting the search criteria, regardless of whether the lines contain transition probability data or energy level classifications.
If the corresponding radio box is selected, the bibliographic references for transition probabilities (TP) and spectral lines will be shown in two separate columns.
The default is to display wavelengths in:
Vacuum (< 2,000 Å), Air (2,000 Å to
10,000 Å), Vacuum (> 10,000 Å).
For wavelength ordered output, the wavelengths are output in one column, with table headings changing as needed to reflect the change in units.
For multiplet ordered output, the wavelength are ALWAYS given in vacuum.
Alternative choices are:
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
By default, Aki (or gkAki)
are displayed in units of s-1. They can be displayed in units
of 108 s-1 if a proper checkbox is checked.
To suppress display of the Relative Intensity columns of data, the
corresponding checkbox can be unchecked.
Although fik, S, and log(gf) values are not displayed by default, if the corresponding checkboxes are clicked, then those data values will be displayed.
To suppress display of the information listed above, the corresponding checkbox can be unchecked. If the user has selected the "Only lines with transition probability data" interest option, then the g values will be suppressed.
Selecting Spectra for Lines
SearchesIf the user has not provided enough information to specify spectra, an error message will be displayed.
| 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 | All Stages of Iron | |
| he | All Stages of Helium | |
| C I, N II, O III | List of spectra specifying neutral carbon, nitrogen II, and oxygen III. |
Plotting Java Grotrian diagramsWorking with the Grotrian diagram plot
Basically, only a computer mouse and a space bar are used for interaction
with this plot.
Default view
Initially all levels and transitions are shown on the plot.
Each energy level is shown by a horizontal bar. The colors (black and blue)
have no meaning and used simply to help with visualization of the plot. The
X-axis corresponds to different level series, and the Y-axis shows the level
energy in cm-1. The radiative transitions between the levels are
shown as the gray lines. The ionization limits are shown as the magenta
horisontal lines. On the top of the plot, the total number of levels, lines and
ionization limits is displayed. This parameters are automatically updated when
zooming in or out. In the bottom right part of the plot, the maximal and
minimal values of the transition probability for the displayed lines are given
in the input text fields. The "Submit" and "Reset" buttons are used for setting
the limits for transition probabilities while the "Isolate" button is used to
single out one level and all relevant transitions. The green field ("zoom field"
below) next to the Y-axis is use for zooming in and out. Below, the top right
part of the plot will be referred to as the "info field".
Output for Lines
The output on the screen is graphical by default, but a significantly
faster ASCII format may also be selected.
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 Javascript language
is enables 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 brown asterisk
and pink plus symbols (see below).
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 2000 Å and above 20000 Å, with air wavelengths in between.
Indexes of refraction are derived for expressions given by
E.R. Peck and K. Reeder, J. Opt. Soc. Am. 62, 958 (1972).
These authors fitted data between 1850 Å and 17000 Å.
Any transition between air and vacuum entails an ambiguity near the transition
point. For example, a wavelength of 2000.648 Å in vacuum
corresponds to 2000.000 Å in air (15 °C in "standard
air," i.e., 101 325 Pa pressure, with 0.033 % CO2).
Conversely, an air wavelength of 1999.352 Å corresponds to
2000.000 Å in vacuum. In this database, as the default the
following convention is adopted in terms of the energy difference or
wavenumber, "
=Ek-Ei":
ForThus, if the tabulated wavelength lies within 2000 ± .648 Å, one must check the energy difference to ascertain whether it is for vacuum or air.![]()
50,000 cm-1
vacuum wavelengths,
For 5000 cm-1 << 50,000 cm-1
air wavelengths,
For![]()
5000 cm-1
vacuum wavelengths.
An explanation of the number of decimal places in each wavelength is provided in the section on significant figures.
Significant Figures
"Ritz" wavelengths are derived from level energies via the Ritz principle: The
wavelength in vacuum is equal to the inverse of the difference in energies,
, between the upper and lower energy
levels of the transition:
= 1/
,
where the wavenumber
= Ek - Ei. The energies
Ek and Ei are of the upper and lower levels of the
transition, respectively. The units of this derived wavelength are the inverse
of the energy units. For example, if the energy units are in inverse
centimeters (cm-1), the Ritz wavelength, derived by taking the
inverse of Ek - Ei, is in cm. One multiplies a
wavelength in cm by 107 to obtain nanometer units, or 108
to obtain ångströms.
The problem addressed here is to express the Ritz wavelength with a precision
comparable to that of the energy difference from which it is derived. Because
the wavelength and difference in energies are inversely related, a given number
of significant figures does not always correspond to the comparable precision
for both. For example, if the energy difference
is 0.99, an extra significant figure is required to express the
Ritz wavelength of comparable precision: 1.01.
The number of significant figures of any number, X, is equal to [log10(X)] + dp +1, where dp indicates the number of decimal places and the square bracket indicates the integer value without roundoff, e.g., [5.6] = 5. Using this, we set the significant figures equal to one another, except for a "shift" between them to account for the fact that they are inversely related:
)]
+ dp
= [log10(
)
+
]
+ dp
.
Here
indicates a shift between the
two quantities to account for the fact that they are inversely related. In the
above expression, the units of
are
physically reasonable for values of this shift range from 0 to 1, and the
chosen value depends on the criteria one applies. The number of decimal places
in the energy difference, dp
, is set to the smaller of the dp's for the lower and
upper level energies of the transition. Applying the relation between
and
to the above expression, one obtains:
(cm)
= [2log10(
)
+
]
+ dp
.
If
= 0, dp
will yield a sufficient number of
significant figures such that when the derived wavelength is inverted, in all
cases the resulting
will be no less
precise than the original
from which
the wavelength was derived. Unfortunately, this choice often yields an overly
optimistic precision for the derived wavelength. We have chosen
= 0.5 as a compromise between
full inversion precision and realistic precision in the derived wavelength. In
the large majority of cases, the error in
upon inverting the derived wavelength is at most 1 in the last
decimal place. This factor of 0.5 corresponds to a shift of half a decade,
which is intuitively reasonable for two quantities that are inversely related.
Thus the expression we use in determining the number of decimal places in the
derived Ritz wavelength is:
(Å)
= [2log10(
)
- 7.5] + dp
.
If dp
is negative, we set
the actual number of decimal places to zero and replace the final
dp
digits in the integer
part of the wavelength with zeros.
In general, the uncertainty of the last significant figure can be as
large as 9.
When the wavelengths are calculated online from the available
energies of the lower and upper levels, either asterisk "*" or plus "+"
is appended to the wavelength value. The former simply indicates that
this value was calculated online, while the latter points out that a
number of zeros in the energies were not accounted for in the
wavelengths calculation and therefore the actual accuracy of this
particular wavelength may be higher.
, (in place of or in addition to
wavelengths), this quantity is calculated from the level energy
differences when they are available for both the lower and upper level.
When either the lower or upper energy is not available, each transition
wavenumber is calculated from the wavelength. The most common cases in
ASD of transitions without available energy level information occur for
elements with Z > 28. Because these wavelengths are
typically truncated, the uncertainty in the last significant figure is
negligible. Thus we set
in
the above expressions to zero, and use the following expression:
= [2log10(
)]
+ dp
.The following points should be kept in mind when using the relative intensities:
Descriptors to the relative intensities have the following meaning:
* Intensity is shared by lines differing only by J.
: Observed value given is actually the Ritz value rounded to 0.1 Å, e.g., Ne I.
= Multiply classified line.
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 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 estimated.
H Very hazy line.
hf Line has hyperfine structure.
l Shaded to longer wavelengths; NB: This looks like a "one" at the end
of the number!
m Masked by another line (no wavelength measurement).
p Perturbed by a close line.
r Easily reversed line.
s Shaded to shorter wavelengths.
w,d Wide, diffuse, hazy, etc.
x Extrapolated wavelength.
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
NkAkih
ik,
ik is the photon
energy (or the energy difference between the upper level and lower level).
Although both Aki and
ik 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.
Either transition probability "Aki" (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 units of s-1.
- fik is the absorption oscillator strength or f-value.
- fik = Aki · 1.4992 10-16 gk/gi
2, for all multipole types,
- where
is the wavelength in ångströms
- log(gf) is the log10(gi fik), 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.
| AA | ≤ | 1% |
| A+ | ≤ | 2% |
| A | ≤ | 3% |
| B+ | ≤ | 7% |
| B | ≤ | 10% |
| C+ | ≤ | 18% |
| C | ≤ | 25% |
| D+ | ≤ | 40% |
| D | ≤ | 50% |
| E | > | 50%. |
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.
3
3
5
5
is the wavelength in ångströms 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.
|"(or "|" in the output ASCII
file) indicates a fully interpreted level lacking an appropriate
configuration and/or term designation because of a strongly mixed
eigenvector composition. For ASCII output, periods are inserted whenever
necessary to avoid ambiguity due to the lack of superscripts, and
brackets enclose J values of the parent term.
Online: March 1999 - Last update: September 2005 |
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