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Published on: October 18, 2018
Vibrationally resolved photoelectron spectroscopy of oligothiophene radical anions
Glen K Thurston1, Cole R Sagan1, Etienne Garand1
1Department of Chemistry, University of Wisconsin-Madison, 1101 University Ave., Madison, Wisconsin 53706, USA.
Abstract:
Vibrationally resolved photoelectron spectroscopy of terthiophene, quaterthiophene, and quinquethiophene radical anions is presented. The increased spectral resolution afforded by the combination of slow photoelectron velocity-map imaging and ion cooling in a cryogenic ion trap allows the characterization of vibronic structures within the S0 and T1 states. Analysis of the spectra, aided by electronic structure calculations and Franck-Condon simulations, revealed evidence for significant contributions from kinetically trapped higher energy conformers in the anion-to-triplet transitions. Unlike the lowest energy structures, where all the thiophene linkers are in the trans configuration, these higher energy conformers contain at least one cis linker. We also found that the adiabatic Franck-Condon simulations drastically underestimated the intensities of some vibronic features in the singlet ground state spectra due to large geometry changes upon photodetachment and anharmonic couplings in the singlet state.
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Stretching vibrations are vibrational motions that occur along the bond line, changing the bond length or distance between two bonded atoms. They are further distinguished as symmetric or asymmetric. In symmetric stretching, the...

