Revised fast-track proposal on wavelength passes DMG review

[James Hester]

Please note the following message from the chair of the core DMG regarding
the fast-track proposal to define a
_diffrn_radiation_wavelength_determination data item.  Under the fast-track
system, if no unresolvable objections are received from COMCIFS within the
next 6 weeks, the proposal will be accepted.

James.

(message from core DMG chair follows)

 Dear Colleagues,

Last September I circulated for fast track approval a recommendation for
adding a new item:

                 _diffrn_radiation_wavelength_nominal,

to the core dictionary (see below for details).  The intent was that this
could be used for giving a nominal wavelength calculated e.g., from the
parameters of a diffractometer.  It was proposed that this might be needed
for completeness even though it was not accurate enough for calculating
lattice parameters, etc.  This proposal was passed by the core CIF
dictionary maintenance group by default (no one raised any objection).  When
this proposal was subsequently presented for final approval to COMCIFS, Nick
Spadaccini suggested a more elegant alternative, namely that by adding
instead the item

        _diffrn_radiation_wavelength_determination

we could loop the nomiinal wavelength with the  refined (and any other
interesting) wavelengths.  This would be more informative and allow for
future expansion.

An example of how this might be used is:

         loop_
             _diffrn_radiation_wavelength_id
             _diffrn_radiation_wavelength
             _diffrn_radiation_wavelength_determinaton
                1   1.23456   fundamental
                2   1.25      estimated

According to our rules, this proposal was posted for comment to the coreCIF
dictionary maintenance group for six weeks.  Two comments were received,
neither raising any serious objection

David Brown
Chair Core CIF Dictionary Maintenance Group

COMMENTS FROM CORE CIF DICTIONARY MANAGEMENT GROUP
--------------------------------------------------

Comment from Jim Kaduk
I think this enumerated data item gets us to where we want to be.  We
want to document the wavelength(s) used in the experiment, as well as
how it was determined.  Knowing both, one could change/correct the
wavelength later if desired for some particular purpose.

Comment from R. Curtis Haltiwanger
Research Scientist
Cephalon, Inc.
610-738-6853

As I said I have only used lab sources, so I have not needed other
wavelengths.
That makes it hard for me to comment on this further extension.
In general, I like including additional information.
Probably because of my lack of experiance this extension seems complicated
to me.
I'll leave it to others to comment and evaluate.


PROPOSED DICTIONARY CODE
------------------------

Add new item to DDL1 Core CIF dictionary

data_diffrn_radiation_wavelength_determination
  _name                      '_diffrn_radiation_wavelength_determination'
  _category                    diffrn_radiation_wavelength
  _type                        char
  _list                        both
  _list_reference            '_diffrn_radiation_wavelength_id'
 loop_
   _enumeration
   _enumeration_detail
     'fundamental'
 'Wavelength that is a fundamental property of matter e.g. MoK\alpha'
     'estimated'
 'Estimated from secondary information e.g. monochromator angle or time of
flight'
     'refined'
 'Based on refinement using a standard material with known cell parameters'

  _definition
;              The method of determination of incident wavelength. Further
information may be provided in _diffrn_radiation_special_details
;
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