The electronic spectra of 2- chlorothiophene and 3-chlorothiophene in the vacuum ultraviolet photoabsorption energy region (3.9–10.8 eV)

The absolute photoabsorption cross-sections for 2-chlorothiophene (2-Cl-Th) and 3-chlorothiophene (3-Cl-Th), in the 3.9–10.8 eV energy range, were recorded for the first-time using synchrotron radiation. New ab initio theoretical calculations performed at the time-dependent density functional theory (TD-DFT) level were used to help interpret the photoabsorption spectra. These have provided important information on the nature of the excited states which have been assigned to valence, mixed valence-Rydberg and Rydberg transitions. The combination of high-resolution vacuum ultra-violet synchrotron radiation with TD-DFT, represents the most comprehensive and self-consistent assignment of the chlorothiophenes electronic excitation to date. Photolysis lifetimes in the Earth^{\prime}s upper atmosphere for both chemical compounds have been estimated from the absolute photoabsorption cross-sections. Potential energy curves have been obtained at the TD-DFT level of theory, showing that the dissociative character of the lowest-lying electronic states is more efficient in 3-Cl-Th.