NAME

       Xray::Absorption::CL - Perl interface to the Cromer-Liberman tables

SYNOPSIS

          use Xray::Absorption;
          Xray::Absorption -> load("cl");

       See the documentation for Xray::Absorption for details.

DESCRIPTION

       This module is inherited by the Xray::Absorption module and provides access to the data
       contained in the Cromer-Liberman tables of anomalous scattering factors and line and edge
       energies.

       The data in this module and the Fortran code which it calls as a shared library, referred
       to as "The CL Tables", was published as

         S. Brennan and P.L. Cowen, Rev. Sci. Instrum, vol 63,
         p.850 (1992)

       More information about these data is available on the Web at

          http://www.slac.ssrl.stanford.edu/absorb.html.

       The values for the anomalous scattering factors are calculated by calls to the Ifeffit
       library by Matt Newville.

       The values of edge and line energies are contained in a database file called cl.db which
       is generated at install time from the flat text files of the these data.  The data is
       stored in a Storable archive using "network" ordering.  This allows speedy disk and memory
       access along with network and platform portability.

       The required "File::Spec", "Chemistry::Elements", "Storable" are available from CPAN.

METHODS

       The behaviour of the methods in this module is a bit different from other modules used by
       "Xray::Absorption".  This section describes methods which behave differently for this data
       resource.

       "get_energy"
           Example:

              $energy = Xray::Absorption -> get_energy($elem, $edge);

           This behaves similarly to the "get_energy" method of the other resources.  When using
           the CL data resource, $edge can be any of K, L1-L3, M1-M5, N1-N7, O1-O7, or P1-P3.
           Line energies are not supplied with the CL data set.  The line energies from the
           McMaster tables are used.

       "cross_section"
           Example:

              $xsec = Xray::Absorption -> cross_section($elem, $energy, $mode);

              @xsec = Xray::Absorption -> cross_section($elem, \@energy, $mode);

           For this data resource, one call in list context is considerably faster than repeated
           calls in scalar context.  It is well worth the trouble of organizing your code to make
           a single call in list context and store the results for later use.

           This behaves slightly differently from the similar method for the McMaster and Elam
           resources.  The CL tables are actually tables of anomalous scattering factors and do
           not come with coherent and incoherent scattering cross-sections.  The photo-electric
           cross-section is calculated from the imaginary part of the anomalous scattering by the
           formula

                mu = 2 * r_e * lambda * conv * f_2

           where, "r_e" is the classical electron radius, lamdba is the photon wavelength, and
           conv is a units conversion factor.

                r_e    = 2.817938 x 10^-15 m
                lambda = 2 pi hbar c / energy
                hbar*c = 1973.27053324 eV*Angstrom
                conv   = Avagadro / atomic weight
                       = 6.022045e7 / weight in cgs

           The $mode argument is different here than for the other resources.  The options are
           "xsec", "f1", and "f2", telling this method to return the cross-section or the real or
           imaginary anomalous scattering factor, respectively.

           The values for f1 and f2 are computed by linear interpolation of a semi-log scale.
           Care is taken to avoid the discontinuities at the edges.

           Because the CL tables do not include the coherent and incoherent scattering terms, the
           value returned by "get_energy" is a bit smaller using the CL tables than using the
           others.

EDGE AND LINE ENERGIES

       The CL data resource provides a fairly complete set of edge energies.  Any edge tabulated
       on the Gwyn William's Table of Electron Binding Energies for the Elements (that's the one
       published by NSLS and on the door of just about every hutch at NSLS) is in the CL data
       resource.  The CL data comes with the same, limited set of fluorescence energies as
       McMaster.

BUGS AND THINGS TO DO

       None that I know about...

AUTHOR

         Bruce Ravel, bruce@phys.washington.edu
         http://feff.phys.washington.edu/~ravel/software/Absorption