Using the X-ray Absorption Data Library¶
The X-ray Absorption Data Library (xaslib) website https://xaslib.xrayabsorption.org presensts tools to browse and view a collection of X-ray Absorption Spectroscopy (XAS) data held by The International X-ray Absorption Society. The main web page will show a periodic table for browsing spectra by absorbing element:
Clicking on any of the element symbols will show a list of spectra for that element. The form on the right hand side allows further refinement of the displayed spectra, based on which Edge, Beamline, Measurement Mode, Rating, or Text found in the information for the spectra.
As an example element with a relatively small number of spectra, clicking on V will show a table with 5 spectra for vanadium:
Here, the table shows spectrum name, Edge measured, the Beamline used, and an optional Rating for each spectrum.
Clicking on the name of any of the spectra will take you to a page dedicated for that spectrum, as discussed below. There are also buttons to the right of the spectra table to “Plot Spectra” and “Save Zip File” for spectra selected with the check-boxes. You can use the “Select All” and “Select None” links to fill in all or none of the checkboxes. Clicking on “Select All” and then “Plot Spectra” will bring up a page with an interactive plot of the 5 selected spectra. This will look like this:
This plot is interactive in a few ways:
1. hovering your mouse over the plot will bring up a small toolbar allowing you zoom in, zoom out, pan, reset the scale, and save an image of the plot.
2. clicking and dragging will zoom in on a portion of the plot. You can double-click to zoom out, or use the toolbar.
3. clicking on the entries in the legend (for example the label with the blue line and V2O3) will toggle whether that spectra is shown or hidden in the plot.
This allows you to interactively zoom in to better see the differences in the V XANES:
Returning to the main page (using the browser’s “back” button will return to the earlier page of selected spectra), where you can also use the “Save Zip File” to download a zip file with the data files for the selected spectra.
The XAS Spectrum¶
The data in xaslib contains several kinds of information. The most important of these is the XAS Spectrum. This contains an XAS spectrum \(\mu(E)\), which is to say arrays of numbers for Energy and Absorbance, and a set of meta-data that goes along with each spectrum to help describe it the important details needed to use these data. The full details of what metadata is stored and how will be given in Database Design for the XAS Data Library, and the emphasis here will be on using the web library.
Clicking on any of the spectra listed in the Spectrum Table, such as shown in Fig Spectra selections for vanadium will bring up a page with lots of the information for that spectrum, like this:
The main component of the individual XAS spectrum is the basic type of data presented in X-ray Absorption Data Library. Each spectrum represents \(\mu(E)\), the X-ray absorption coefficient, typically measured in transmission mode. They consist of at least two arrays of numerical data with all arrays having the same number of data points (typically a few hundred data points). These arrays