Dear Bernhard,

Here are calculated reduced partition function ratios (RPFR)
for siderite:

273.16 K   ln(RPFR) =  0.11549
298.16                        0.10072
373.16                        0.06995
473.16                        0.04659
573.16                        0.03309

Source: Richard H. Becker(1971) ,  Ph D Thesis,  The University of
Chicago.
You can combine these data with experimental values of RPFR for
water to calculate fractionation factor. The most updated values
for water you can find in paper by Horita and Wesolowski, GCA
1997+/-1. You can also find  ln(RPFR) for water in  Hattori K. and
Halas S. (1982), GCA,pp. 1863-1868.
Regards,
Stan


==============================
Professor Dr. Stanislaw Halas
Mass Spectrometry Laboratory
Maria Curie - Sklodowska University
20-031 Lublin, POLAND
tel: (48 81) 537 6275    fax: (48 81) 533 3669