Simulation of high pressure diffraction patterns: Chi files

Chi files are ascii files. They are popular in high pressure science because they can be created from 2-D diffraction images using Fit2d. Basically, they contain a diffraction pattern and look like this:

Ag6401_3001.stl: Azimuth/2-theta
2-Theta Angle (Degrees)
Intensity
       1519
 9.0983873E-03  0.0000000E+00
 2.7295163E-02  1.0432003E+04
 4.5491938E-02  4.5617261E+03
 6.3688710E-02  1.5208940E+03
 8.1885487E-02  4.7980701E+02
 1.0008226E-01  1.5759076E+02
 1.1827904E-01  8.9839554E+01
 1.3647582E-01  5.8592739E+01
 2.6385325E-01  3.8000801E+01
 2.8205001E-01  3.1565350E+01
 3.0024680E-01  2.8543026E+01
 3.1844357E-01  2.3427414E+01
 3.3664036E-01  1.8689501E+01
 ....

The first line is a comment, the second line tells you what's in the first column, the third line tells you what's in the second column, and the fourth line gives you the number of datapoints. Atfer, you simply have the data, in ASCII. In this case, it's diffraction intensity vs. 2 theta.

The HPDiff applet can read Chi files with 2theta-intensity data and overlay them with the synthetic diffraction patterns. It's quite usefull for quick and dirty peak identification and pressure calibration.