Clemens Vonrhein vonrhein at
Mon Aug 16 09:52:59 EST 1993

Dear Crystallographers!

Here are some 'nice' little questions about a special case of
non-crystallographic symmetry:
How can I detect a twofold NCS, which is parallel to a crystallographic
twofold axis? I think, that I will see a very high peak on a Harkerplane in
my Difference Patterson. But how can I get the coordinates of the
translation of this NCS in respect to the origin (out of this high peak an
the Harkerplane)? What exactly are pseudo-Harkerplanes? What will be the
symmetry of this pseudo-Harkerplane (how to determine it)?

The problem is, that the pseudo-Harkerplane is perpendicular to a
crystallographic 2(1) axis, so that it is difficult to know if it is really
a crystallographic 2(1) with a 2fold NCS or a crystallographic 2 with a
2(1)-NCS. A lot of tricky problems, as you can see. Any sugestions? Or is
there any good book about the whole NCS-business?

Thanks very much


P.S. If anything interesting turns up, I will post a follow-up.

* Clemens Vonrhein   email:vonrhein at *
*								*
*       Institut f"ur Organische Chemie				*
*         und Biochemie						*
*       Abt. Prof. G.E.Schulz					*
*       Albertstr.21						*	
* D-79104 Freiburg i.Br., Germany				*

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