Line Identification
The line identification module can - unsurprisingly - be used to identify emission lines. This is done by comparison between the measured spectrum and the position and intensity of spectral lines according to the NIST atomic spectra database (NIST asd).
The spectra fetched from the NIST asd are selected via text input at the top of the module. Spectroscopic notation is used, which means that the element is selected by its chemical symbol (i.e. Ar for Argon or Fe for Iron) followed by a space and then a Roman numeral indicating the ionization state (e.g. Ar I for argon neutrals, or Ti III for titanium doubly charged ions). Multiple ionization states can be selected at once by separating them with a minus sign (i.e. Ar I-IV for all lines of argon neutrals and ions with charge states 1 to 3). Multiple emitters can be chained together using a comma (e.g. Ar I, Ti II selects lines of argon neutrals and lines of titanium singly charged ions together).
From the line position and the relative intensity tabulated in the NIST asd, a stick spectrum is calculated that can be compared to the experimental data to identify the lines. For example, the screenshot below clearly shows that the leftmost line is the emission of hydrogen neutrals, while the rest corresponds to argon neutrals.
Instead of using the relative intensity values tabulated by the NIST asd, the intensity can also be calculated using LTE. Changing the drop-down menu reveals an input field for the electron temperature. After changing any of the settings, pressing "Display" updates the calculated stick spectrum to the new values. Fitting the spectrum to obtain the excitation temperature is currently not supported. The library that powers this module, owlspec documents an example of how to do this in simple python code.
Note
When using LTE line intensities, lines for which base data (
The table at the bottom of the module tab shows the data obtained from NIST asd, for reference.
The identification tab uses owlspec to fetch the data listed by the NIST Atomic Spectra Database. These can be cited as follows:
- Julian Held: (2024) owl spectroscopic library (v0.3.0) https://doi.org/10.5281/zenodo.11002438
- Kramida, A., Ralchenko, Yu., Reader, J. and NIST ASD Team (2023). NIST Atomic Spectra Database (version 5.11). Available: https://physics.nist.gov/asd [Sat Apr 20 2024]. National Institute of Standards and Technology, Gaithersburg, MD. DOI: https://doi.org/10.18434/T4W30F
Up to date citation information for NIST ASD is provided here: https://physics.nist.gov/PhysRefData/ASD/Html/verhist.shtml