ASCII format data files are plain text files which can be manipulated by many programs, including text editors, and stand-alone plotting routines. These files can be easily moved between different programs, different operating systems, and different machines. They can be sent by e-mail.
The ASCII files used by the UWXAFS data analysis programs have a
minimal but well-defined layout, based on the lines of the text file.
Document lines are placed at the top of the file. There can be any
number of these lines, though most programs will store only the first
20 lines and ignore the rest. After the document lines, there is a
line with minus signs (----) to indicate that all the document
lines have been written. (If you want to get picky, the second through
sixth non-blank characters in this line must be minus signs.) After
this line of minus signs, there is an ignored line, which is typically
used for labeling the columns of the numerical data which follow. All
of these lines of text may have a number sign # in the first
column. These are put there as a comment line for other programs that
use text files. When read by UWXAFS programs, this leading #
will not read as part of the document line.
After the ignored line for column labels comes the numerical data. Each set of data occurs on a single line. There can be between two and five columns of numbers. Columns of data are separated by one or more spaces or tab characters. The first column contains the abscissa, the second column contains the real part of the ordinate. The third through fifth column (if given) contain the imaginary part of the ordinate, the magnitude of the ordinate, and the phase of the ordinate, respectively. Listing all forms of complex data is redundant but quite useful. The UWXAFS programs will write all five columns for any complex data (as for chi(R) and chi(q)). The UWXAFS data analysis programs limit the data size to 2048 data points, which should be sufficient for all XAFS analysis.
The leading # in the first column of text lines and the general format
of the ASCII format works well with the general-purpose, stand-alone
graphics program comp.graphics.gnuplot.
As with the UWXAFS binary files, the ASCII files have a file type
associated with them (see the next chapter for more details), though the
only purpose of the file type of ASCII files is to tell how many columns to
use. For ASCII files with file type xmu or chi only the first two
columns are used, and the rest are ignored. All other file types (rsp
and env) indicate complex data, so that all five columns are used.
Examples of each of the file types are given in the following sections.
Files with xmu File Type contain absorption data on an energy
grid which does not need to be evenly spaced. The units of energy are
eV. This file type is used for raw absorption data input to
xmu files contains values of
absorption. The units for the data in the second column are
unimportant. Raw synchrotron data of detector intensities must be
converted to xmu format before being used in xmu data
files. Here is part of one of them:
# Cu foil, 10K
# data taken at NSLS beamline X-11A Sept 1992
# foil from 99.999% Cu rolled and annealed to ~12 microns
#----------------------------------------------------------
# energy xmu
0.8968871E+04 0.9484839E+00
0.8969347E+04 0.9510049E+00
0.8969909E+04 0.9537250E+00
0.8970386E+04 0.9559226E+00
0.8970862E+04 0.9591411E+00
Files with chi File Type contain chi(k) data. The first column
contains k-values in units of inverse Angstrom. These values
should be evenly k-spaced. All UWXAFS programs will write
chi files with a grid spacing of delta k = 0.05 inv. Ang.,
and will interpolate any input chi files onto this grid. The
second column of a chi file contains the chi(k) values. It
does not contain k-weighted chi(k). Any data past the second
column will be ignored. The Cu chi(k) data that is output from the
chi data files. Here is part
of one of them:
# data : cu 10k background by autobk
# chi: skey ASCII of cu010k.dat using skey ASCII of chi.dat
# e0 = 8982.61; pre-edge range =[ -50.0 -200.0]; edge step = 2.257
#---------------------------------------------------------------------
# k chi(k)
.5000000E+00 -.1540712E+00
.5500000E+00 -.1576023E+00
.6000000E+00 -.1621443E+00
.6500000E+00 -.1669036E+00
.7000000E+00 -.1723104E+00
.7500000E+00 -.1756163E+00
.8000000E+00 -.1719365E+00
.8500000E+00 -.1712734E+00
.9000000E+00 -.1738329E+00
.9500000E+00 -.1679564E+00
.1000000E+01 -.1598812E+00
Files with rsp File Type contain chi(R) data. The first column
contains R-values in units of Angtroms. These values will be
evenly R-spaced. Though the size of the grid can vary, it will
typically be delta R = 0.031 Ang.. The second, third, fourth,
and fifth columns of an rsp file contains the real, imaginary,
amplitude, and phase parts of chi(R), respectively. The
R-space outputs from rsp data
files. Here is part of one of them:
# data : cu 10k background by autobk
# chi: skey ASCII of cu010k.dat using skey ASCII of chi.dat
# e0 = 8982.61; pre-edge range =[ -50.0 -200.0]; edge step = 2.257
#---------------------------------------------------------------------
# r real(chi(r)) imag(chi(r)) ampl(chi(r)) phase(chi(r))
.0000000E+00 .6142655E-01 .0000000E+00 .6142655E-01 .0000000E+00
.3067962E-01 .2903621E-01 -.5033424E-01 .5810884E-01 -.1047559E+01
.6135923E-01 -.2831294E-01 -.4127166E-01 .5004970E-01 -.2172074E+01
.9203885E-01 -.4082767E-01 .1267206E-01 .4274903E-01 -.3442544E+01
.1227185E+00 .3410820E-02 .4164495E-01 .4178440E-01 -.4794109E+01
.1533981E+00 .4358866E-01 .1037124E-01 .4480551E-01 -.6049594E+01
.1840777E+00 .2678454E-01 -.3571878E-01 .4464575E-01 -.7210562E+01
.2147573E+00 -.2032813E-01 -.3259343E-01 .3841307E-01 -.8411637E+01
.2454369E+00 -.2877361E-01 .1295394E-01 .3155512E-01 -.9847800E+01
.2761165E+00 .1427407E-01 .3249273E-01 .3548981E-01 -.1140950E+02
Files with env File Type contain backtransformed EXAFS date
chi(q). The first column contains k-values in units of
inverse Angstroms. These values will be evenly k-spaced, with
delta k = 0.05 inv Ang. The second, third, fourth, and fifth
columns of an env file contains the real, imaginary, amplitude,
and phase parts of chi(q), respectively. The backtransformed
k-space outputs from env
data files. Here is part of one of them:
# data : cu 10k background by autobk
# chi: skey ASCII of cu010k.dat using skey ASCII of chi.dat
# e0 = 8982.61; pre-edge range =[ -50.0 -200.0]; edge step = 2.257
#---------------------------------------------------------------------
# k real(chi(k)) imag(chi(k)) ampl(chi(k)) phase(chi(k))
.5000000E+00 .7191563E-01 -.2600794E-01 .7647399E-01 .5936174E+01
.5500000E+00 .6291400E-01 .1202853E-01 .6405354E-01 .6472096E+01
.6000000E+00 .3789376E-01 .4072316E-01 .5562655E-01 .7104558E+01
.6500000E+00 .2566442E-02 .5404260E-01 .5410350E-01 .7806528E+01
.7000000E+00 -.3530601E-01 .4896256E-01 .6036428E-01 .8478718E+01
.7500000E+00 -.6737898E-01 .2606567E-01 .7224505E-01 .9055658E+01
.8000000E+00 -.8631523E-01 -.1053911E-01 .8695626E-01 .9546277E+01
.8500000E+00 -.8719383E-01 -.5396802E-01 .1025442E+00 .9979011E+01
.9000000E+00 -.6847088E-01 -.9584310E-01 .1177886E+00 .1037525E+02
.9500000E+00 -.3230590E-01 -.1278652E+00 .1318832E+00 .1074810E+02
.1000000E+01 .1581111E-01 -.1433793E+00 .1442484E+00 .1110541E+02