Ansys Chemkin expects the thermodynamic data to be provided in a specific format. In addition to the fourteen polynomial fitting coefficients (described in Standard-state Thermodynamic Properties in the Chemkin Theory Manual), the database also contains the species' name, its elemental composition, its electronic charge, and an indication of its phase (gas, liquid or solid). The data for each species requires four formatted lines of length 80 characters. Figure 2.1: Excerpts from the therm.dat Thermodynamic Database File is a sample of the lines required for a species and Table 2.1: Summary of the Rules for Thermodynamic Data provides a detailed specification of the format required for entry of thermodynamics data. The first two lines in Figure 2.1: Excerpts from the therm.dat Thermodynamic Database File are required at the top of a thermodynamic database file; the first line specifies that the following is a set of thermodynamic data, while the second line provides the three temperatures used in the fitting process (a low temperature, break temperature, and high temperature). You must also adhere to these specifications when placing thermodynamic data within the Gas-phase Kinetics or Surface Kinetics input file.

Ansys Chemkin allows two salient formats based on the number of coefficients used in fitting the data: 7-coefficient and 9-coefficient. In the Ansys Chemkin documentation, the latter is referred to as the NASA9 format, acknowledging its origin. In this chapter, details of the 7-coefficient format are presented first, while the specifics of NASA9 usage in Ansys Chemkin are described in Input in 9-Coefficient Format (NASA9).