High-Speed Machine Computation of Ideal Gas Thermodynamic Functions. I. Isotopic Water Molecules

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Abstract
A procedure is developed for the machine computation of the partition functions for non‐rigid rotating anharmonic oscillators. Vibrational‐rotational coupling terms and low temperature rotational corrections are included. A general code has been designed to permit the calculation of the ideal gas thermodynamic functions for a large variety of molecular structures on the National Bureau of Standards Eastern Automatic Computer—SEAC. The method is illustrated by evaluating the thermodynamic functions for an asymmetric top molecule. Tables of Cp0/R, (H0–E00)/RT, (E00–F0)/RT, and S0/R have been evaluated for H2O, HDO, D2O, HTO, DTO, and T2O at close intervals from 50° to 5000°K. The time required for these computations is of the order of several minutes per molecule. The results for H2O are in good agreement with those obtained by direct summation.