Theoretical study on the structure, vibrational frequency and thermodynamic properties of 2,3,7,8-tetrachlorinated dibenzo-p-dioxin

In this paper, semi-empirical molecular orbital method with the PM3 Hamiltonian was used to study the geometrical optimization and thermodynamic parameters of heats of formation, standard entropy, standard enthalpy, heat capacity of 2,3,7,8-tetrachlorinated dibenzo-p-dioxin (TCDD). Density function theory (DFT) method was also employed to further optimize the molecular geometry of 2,3,7,8-TCDD at B3LYP/6-31G, B3LYP/6-31G*, B3LYP/6-311G* and MP2/6-31G* levels, respectively. Harmonic vibrational spectrum have been performed at B3LYP/6-31G* and B3LYP/6-311G* levels. The standard thermodynamic properties at various temperatures have been evaluated using the scaled B3LYP/6-31G* and B3LYP/6-311G* frequencies. Calculated results are compared with each other and with available experimental data, and are discussed in detail.