Thermochemistry in Gaussian The Internal Thermal Energy n

Thermochemistry in Gaussian

The Internal Thermal Energy n The internal thermal energy can be obtaine from the partition function, q. n The contributions to partition functions. n Translational partition function; qt n Rotational partition function; qr n Vibrational partition function; qv n Electronic partition function; qe

Contributions from Translation n Translational partition function n Contribution to internal thermal energy

Contributions from Electronic motion n Electronic partition function n Contribution to internal thermal energy

Contributions from Rotation n Rotational partition function n Contribution to internal thermal energy

Contributions from Vibration n Vibrational partition function n Contribution to internal thermal energy

Symbols

Output from Gaussian n Frequency Calculation n Zero point energy

Thermal Correction n Thermal Correction to Energy n Thermal Correction to Enthalpy n Thermal Correction To Gibbs Free Energy

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

Individual Contributions n Individual contributions to Etot, Ctot and Stot n Individual contributions to partition functions

Example n H-abstraction reaction

Rate of Reaction

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

Heat of Formation