PNNL

Abstract

We report the observation of negative electron binding energies in a triply charged anion, 1-hydroxy-3,6,8-pyrene-trisulfonate (HPTS3–). Low-temperature photoelectron spectra were obtained for HPTS3– at several photon energies, revealing three detachment features below 0 electron binding energy. The HPTS3– trianion was measured to possess a negative electron binding of -0.66 eV. Despite the relatively high excess energy stored in HPTS3–, it was observed to be a long-lived anion due to its high repulsive Coulomb barrier (~3.3 eV), which prevents spontaneous electron emission. Theoretical calculations were carried out, which confirmed the negative electron binding energies observed. The calculations further showed that the highest occupied molecular orbital in HPTS3– is an anti-bonding ? orbital on the pyrene rings, followed by lone pair electrons in the peripheral –SO3– groups. Negative electron binding energy is a unique feature of multiply-charged anions due to the presence of the repulsive Coulomb barrier. Such metastable species may be good models to study electron-electron and vibronic interactions in complex molecules.