Anion Resonances and Autodetachment Dynamics of Fluoranthene.

Anion resonances could play a key role in anion formation by electron attachment to polycyclic aromatic hydrocarbons which are widely considered to be ubiquitous in the interstellar medium. If present in appreciable abundance, anionic species could facilitate many important astrochemical processes in those environments. Here, we probe the energies, lifetimes, and detachment dynamics of the fluoranthene anion resonances using total photoelectron yield (TPY) spectroscopy in combination with resonant photoelectron imaging of cryogenically cooled ions. Our experiments reveal seven anion resonances in the 6000-34,000 cm^-1 range, two of which are optically dark and only observed after being populated via internal conversion from higher resonances. We show that fast autodetachment from the vibrationally resolved lowest-energy resonance is Franck-Condon in nature and that resonances in the ultraviolet region undergo autodetachment into the T₁ neutral state of fluoranthene. Our resonances assignments are well supported by TD-DFT calculations that consider geometry relaxation and zero-point energy effects.