0000000000775321
AUTHOR
Christopher S. Page
A Theoretical Study of the Low-Lying Excited States of trans- and cis-Urocanic Acid
A multiconfigurational second-order perturbation theory (CASPT2) study of the lowest lying states in the gas-phase electronic spectra of trans- and cis-urocanic acid is presented. Geometries of both isomers have been optimized at the MP2/6-31G(d) and π-CASSCF/ANO-L(4s3p1d,2s) levels of theory. The geometries are found to differ considerably between the two levels. The vertical and 0−0 excitation spectra were calculated for each isomer. Both singlet and triplet states are described for each, including the lowest lying ππ* excitations and the nOπ* excitations. Remarkably, in the trans spectrum, it is found that the nOπ* state has a higher vertical excitation energy than the lowest ππ* (5.12 v…
A theoretical study of the low-lying states of the anionic and protonated ionic forms of urocanic acid
A multistate second-order perturbation theory (MS−CASPT2) study of the lowest lying states in the electronic spectra of urocanic acid in vacuo is presented. The anionic trans and cis isomers, as well as the biologically important trans protonated ionic structure, are considered. The vertical and 0−0 excitation spectra were computed for each system at the MS−CASPT2/ANO-L level, describing the lowest lying ππ* and nπ* singlet and triplet states. In all three systems, a weakly absorbing ππ* singlet state was observed at ∼4.0 eV in the vertical excitation spectrum, suggesting both a novel assignment and an alternative explanation for the previously described wavelength dependent photochemistry …