help to plotting X-ray diffraction spectrum I=f(θ), Bragg's law

[roben nano]

hello ,
I want to transform file q vs I(q) "*TiO2.dat*"  file obtained by *Calculate 
and print the coherent X-ray diffraction spectrum* to file 
intensity=f(teta) like this spectrum

determined by Bragg's law: 
[image: 2d \sin \theta = n \lambda]


<https://lh5.googleusercontent.com/-y7XUD2IPJ4M/U16MVqnopLI/AAAAAAAAAAg/KGX2obcbhog/s1600/XRD.png>


my best regards 
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