-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1
Please some one tells me if I'm wrong ... but I though that indeed one
is NOT supposed to measure anomalous difference from reflections h and
h' if those are related by one of the symmetry operator of the point
group...
That is in monoclinic (P 1 2 1, more precisely) , (h, k, l) and (-h,
k, -l) should have the same F ... (in a determinist's world)
Though (h, k, l) and (-h, -k, -l) are likely to be different, and
hence (h, k, l) and (h, -k, l) would show the same difference.
Serge.
Le 26 juin 08 à 18:07, Patrick Loll a écrit :
I've always thought that a Bijvoet pair is any pair for which an
anomalous difference could be observed. This includes Friedel pairs
(h & h-bar), but it also includes pairs of the form h & h', where h'
is symmetry-related to h-bar. Thus Friedel pairs are a subset of all
possible Bijvoet pairs.
This is what Ed and I say in our book, at least (shameless plug);
and you can buy it from Amazon, so it must be right, yes?
Pat
On 26 Jun 2008, at 11:55 AM, Bernhard Rupp wrote:
Dear All,
I wonder about the conventions using Friedel vs Bijvoet pair.
a) there are no differences. As long as h = -h, it's a Friedel
or a Bijvoet pair. They are the same.
b) A Friedel pair is any reflection h = -h including hR = -h, i.e.
including centric reflections.
A Bijvoet pair is an acentric Friedel pair, it can carry
anomalous amplitude differences, whereas centric Friedel
pairs invariably cannot. Actually, Bijvoet pairs (acentric
Friedel pairs) invariably do carry anomalous amplitude
differences.
There is no such thing as no anomalous scattering.
We may elect to ignore it, only.
c) of course, this all assumes absence of anisotropic AS.
def b) seems to be helpful in discussions and make sense given that
absolute
configuration that needs AS signal is somehow associated with
Bijvoet's
work.
Are any authoritative answers/conventions/opinions available on
that ?
Thx, BR
*******************************************************************
Dr. Serge COHEN
GPG Key ID: 0B5CDAEC
N.K.I.
Department of Molecular Carcinogenesis (B8)
Plesmanlaan 121
1066 CX Amsterdam; NL
E-Mail: [EMAIL PROTECTED]
Tel : +31 20 512 2053
*******************************************************************
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.8 (Darwin)
iEYEARECAAYFAkhjxYAACgkQlz6UVQtc2uwBBwCfR9b4dipYF5EYioqA6cpSpHnN
z5QAoK6k0VOu93pJoLfV6bvzJgTAnUCN
=fR+n
-----END PGP SIGNATURE-----
