Computing UV–vis spectra of 1-bromo-1-propene: a comparison of model core potential and all-electron basis sets

Abstract

Vacuum ultraviolet (VUV) spectroscopy can be used to identify different isomers in complicated mixtures of many molecules. In this work, calculated VUV spectra are compared with spectra of experimental mixtures to benchmark appropriate computational methods. Because the benchmark molecule, 1-bromo-1-propene, contains a heavy atom, both all-electron and model core potential basis sets were investigated. Time-dependent density functional theory (TD-DFT) can accurately compute electronic excited states at low-energy excitations and was cross-checked at higher energies against results from the symmetry adapted cluster–configuration interaction (SAC–CI) method. TD-DFT was determined to be satisfactory at low energies; however, excitation energies can deviate by 0.5 eV at high energies. TD-DFT with both all-electron and model core potential basis sets produced satisfactory excitation energies for the lower excited states. This method is also satisfactory at predicting spectra produced experimentally, including a mixture of isomers (cis- and trans-1-bromo-1-propene), with the exception of underestimating oscillator strength.