Hi Carlos
It is more than coincidence - in that the X-rays we use for diffraction
are _chosen_ from the spectrum of X-ray wavelengths that correspond to the
interatomic distances (though this is not the only reason they are
chosen).
X-rays can be thought of as those EM waves with wavelengths from ~0.1 -
100 Angstrom, which conveniently brackets interatomic bonded distances
(from ~0.9 {e.g O-H bonds} - ~3 {e.g. M-M single bonds in metal clusters})
Angstroms. So from this spectrum, we choose those lab sources which have
wavelengths in this range, and "tune" (for want of a snappier word) our
synchrotron sources to give us wavelegths in this range.
If you can find a copy of Stout & Jensen "X-ray Structure Determination -
a practical guide" (either the first or second edition), chapter 1,
sections 1.1 and 1.3 explain this quite nicely, and also why we use lab
sources like copper or molybdenum.
> I have once heard and recently read that "the diffraction event results
> from the fact that both the X-rays wavelength and the atomic distances
> are of the same magnitude". Although such a relation seems appealing I
> am unsure if this is not a mere coincidence. Could someone clarify or
> lead me to a relevant reading.
> Cheers,
> Carlos
>
> --
> **************************************
> Dr. Carlos Frazao
> Crystallography Department
> ITQB-UNL, Av Republica, Apartado 127
> 2781-901 Oeiras, Portugal
>
> Phone: (351)-214469666
> FAX: (351)-214433644
> e-mail: [EMAIL PROTECTED]
> www.itqb.unl.pt
>
Harry
--
Dr Harry Powell, MRC Laboratory of Molecular Biology, MRC Centre, Hills
Road, Cambridge, CB2 2QH
