1H2-16O__VT.pf is the partition function for (1H)2(16O) from Vidler and
Tennyson[1], for temperatures between 10 K and 6000 K. The partition function
is calculated including the nuclear spin degeneracy factor (gns = 3, 1 for
ortho-H2O and para-H2O respectively).

The four columns are those of Table II in Ref [1]:
T       temperature in K
Qint    internal partition sum 
Qint'   first moment of Qint, T(dQint/dT)
Qint"   second moment of Qint, T^2 (d^2Qint/dT^2) + 2Qint'

[1] Vidler and Tennyson, "Accurate Partition Function and Thermodynamic Data
for Water", J. Chem. Phys. 113, 9766 (2000)