I'd rather agree with Miguel.
You certainly have evidence telling your 4-fold is crystallographic
(indexing, cell, ), and you do see it on your k=90 section (of course
also on your 180).
You need to check your k=180 peak heights to compare with the 4-fold
axis: they seem to be so perfectly at 90deg to the 4-fold (and
apparently strong enough...), really suggesting a 422 point group. They
could of course be the result of a 2-fold NCS, "accidentally" at 90deg
of the single 4-fold , but then they should show a significantly lower
height wrt the xtallographic axis; how many mols/ASU are you expecting?
(if the heights are equivalent, you shouldn't automatically rule out a
twinning phenomenon in this PG (twinning law would be kh-l): look at
intensity distribution statistics (CCP4 TRUNCATE gives you several), at
regular solvent fractions they are usually quite revealing...)
hth
ale
Miguel Ortiz-Lombardía wrote:
Unless there is pseudo-symmetry, I would say that the self-rotation
indicates that crystal point group is 422... Did the indexing program
suggested something with this symmetry?
Cheers,
Miguel
2007/8/20, Wim Burmeister <[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>>:
Yanming Zhang a écrit :
> Hi,
>
> Would some experts help me to interpretate the attached self
rotation
> function ps graph? The cell: 84.847 84.847 172.485 P4 indexing. In
> perticular, I was puzzled by:
>
> 1,Does the peak (90 45 180) a crystallographic 2-fold or
> non-crystallographic 2-fold?
> 2,Why there is no crystallographic peak on the section kappa=90?
> Giving P4 space group, there should be some high crystallographic
> 4-fold peaks appear on the section.
>
> It probably takes you only 5 minutes. Your help is greatly
appreciated.
>
> Yanming
Deqr Yanming
The north pole of the diagramm corresponds to the direction of the z
axis. There is well a crystallographic 4-fold (and automatically 2-
fold) peak in this direction. Then there are non-crystallographic
2-fold
axes in the x,y plane, spaced by 45 degrees, as all the peaks
appear to
have the same height.
Greetings
Wim Burmeister
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