Gaussian 09 is the latest version of the Gaussian® series of electronic structure programs, used by chemists, chemical engineers, biochemists, physicists and other scientists worldwide. Starting from the fundamental laws of quantum mechanics, Gaussian 09 predicts the energies, molecular structures, vibrational frequencies and molecular properties of molecules and reactions in a wide variety of chemical environments. Gaussian 09’s models can be applied to both stable species and compounds which are difficult or impossible to observe experimentally.