[Ifeffit] how to import this kind of XAFS data

[Matt Newville]

On Fri, Dec 8, 2017 at 3:00 AM, woschangqiang at 126.com <woschangqiang at 126.com
> wrote:

> Hello, dear everyone.
> I downloaded a XAFS data about mettalic Ru from the website of *ixs.iit.edu
> <http://ixs.iit.edu>*. There are 4 groups of information in the data, and
> each ranges between ~67800 with ~63000 in energy. So how to import the
> data to Athena, and how this kind of data was produced? Does anyone  come
> across this situation? Thanks for your time and help in advance.
>


This data file is a particularly nasty form of data from the Lytle
database.   Each line of data contains consecutive pairs of  AngleSteps Mu

To convert the angle steps to energy, you need to know how many steps there
are in a degree and the lattice constant of the mono crystal used.  Neither
of these are in the file.  I happen to have a good guess that these numbers
should be  8000 steps per degree, and 1.92017 Angstroms.

Still the data are a pain to deal with.  They can be read with Ifeffit too,
but with Larch it goes like this:


    ru = read_ascii('ru.001.txt')
    # flatten array data to [step, mu, step, mu,...]
    dat = ru.data.transpose().flatten()

    # take every 2nd value as angle or xmu
    asteps = dat[0::2]
    xmu    = dat[1::2]
    step2rad = (pi/180)/ 8000  # radians per step
    hc     = 12398.417       # eV Ang
    dspace = 1.92017         # Ang

    energy = hc/(2*dspace)/sin(asteps * step2rad)
    label  = 'energy   xmu   angle_steps'
    header = ['data converted from Lytle database file: %s'  % ru.filename,
              'using  dspace=1.92017, steps-per-degree=8000']

    write_ascii('ru.001.xmu', energy, xmu, asteps, header=header,
label=label)

Resulting converted file attached.

--Matt
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