PNNL

Abstract

The dissociation constants of fumaric acid were extracted from uv-vis spectra in the 10-90°C range. These values were used to extract thermodynamic parameters that showed the temperature effects on the dissociations reactions to be dominantly driven by the solvent. The molar absorption coefficients for the fumaric acid, the bifumarate and fumarate species, can be accurately reproduced with the two-term Gauss-Lorentz equation. Deconvolution of these bands showed strong p-p* transitions for all species and weaker charge-transfer-to-solvent transitions for the charged species. TDDFT calculations were used to identify the most important molecular orbitals involved in the vertical excitations of the fumaric acid species. The electron population and their states of delocalisation were also estimated with topological analyses of the electron density and of the Becke-Edgecombe Electron Localisation Function.