1. Thermochemistry in Gaussian

2. The Internal Thermal Energy The internal thermal energy can be obtaine from the partition function, q. The contributions to partition functions. Translational partition function; q t Rotational partition function; q r Vibrational partition function; q v Electronic partition function; q e

3. Contributions from Translation Translational partition function Contribution to internal thermal energy

4. Contributions from Electronic motion Electronic partition function Contribution to internal thermal energy

5. Contributions from Rotation Rotational partition function Contribution to internal thermal energy

6. Contributions from Vibration Vibrational partition function Contribution to internal thermal energy

7. Symbols

8. Output from Gaussian Frequency Calculation Zero point energy

9. Thermal Correction Thermal Correction to Energy Thermal Correction to Enthalpy Thermal Correction To Gibbs Free Energy

10. Total Energy Total electronic energy = Sum of electronic & ZPE = Sum of electronic & T energy = Sum of electronic & T enthalpy = Sum of electronic & T free energy =

11. Individual Contributions Individual contributions to E tot, C tot and S tot Individual contributions to partition functions

12. Example H-abstraction reaction

14. Rate of Reaction

15. Energies Calculation Atomization energy of molecule Heat of formation of atoms at 0 K (expt.) Enthalpy correction of atomic element Enthalpy correction for molecule Entropy for atoms 25 °C (expt.) Entropy for molecules 25 °C =

16. Heat of Formation