Accurate partition function and thermodynamic data for water

The partition function, Q, of (H2O)-O-16 is calculated by explicit summatio n of about 10 500 experimental vibration-rotation energy levels and very hi gh accuracy estimates are obtained for the specific heat capacity (C-p), th e Gibbs enthalpy function (gef), the Helmholtz function (hcf) and the entro py (S) of gas phase water as a function of temperature. For temperatures ab ove 600 K it is necessary to augment the sum with theoretical estimates of the energy levels. These are obtained from high accuracy variational calcul ations which are extended to dissociation using a model for rotational leve ls based on a Pade approximant. Estimates for the partition function and ot her thermodynamic quantities are obtained for temperatures up to 6000 K and temperature dependent error bars presented. All estimates are highly accur ate with the exception of C-p for T > 5000 K, for which further work is req uired. (C) 2000 American Institute of Physics. [S0021-9606(00)02045-6].