Lifetime of negative molecular ions of tetracene and pentacene with respect to the autodetachment of an electron

Internal conversion outcompetes autodetachment from resonances in the deprotonated tetracene anion continuum

“…A number of recent theoretical studies, on systems that are known to exhibit long-lived anions in the gas phase, have supported this contention by highlighting that the above-threshold resonances of shape character have broad electron acceptance windows. [93][94][95] Experimentally, such a broad window to electron attachment dynamics has been observed across a range of PAH and PAHlike systems, 22,30,38 and has been implied in the present study by virtue of thermionic emission observed at all photoexcitation energies. The broad electron acceptance window arises from a combination of a high density of resonances (increases with increasing PAH size) each with a broad spectral width due to their inherent short lifetimes (e.g.…”

“…22,29 As a specific example, mass spectrometry measurements on tetracene and pentacene have shown the formation of long-lived anions with lifetimes of ~10 ms following capture of electrons with up to ~3 eV of kinetic energy. 30 Internal conversion of an anion resonance converts electronic energy into vibrational excitation, which then becomes redistributed amongst the internal degrees of freedom (intramolecular vibrational relaxation) and leads to a temperature increase of the molecular anion. 31,32 If such an anion is formed under isolated conditions, the total internal energy of the system remains above the neutral ground state and the system may statistically detach the most weakly bound electron on a microsecond to millisecond timescale -known as thermionic emission.…”

Resonances of the anthracenyl anion probed by frequency-resolved photoelectron imaging of collision-induced dissociated anthracene carboxylic acid

“…18,23,24 Electron impact studies have confirmed that such resonance-mediated decay processes occur 23 and ground state anions of tetracene (C 18 H 12 ) and pentacene (C 22 H 14 ) have been observed following electron impact energies of ∼3 eV. 25 …”

Comment on: Negative ions, molecular electron affinity and orbital structure of cata‐condensed polycyclic aromatic hydrocarbons by Rustem V. Khatymov, Mars V. Muftakhov and Pavel V. Shchukin

“…Table shows the ground state AE a for the AHC considered herein, the ionization energies from the NIST database and the lifetimes from the subject article and Khatymov et al There are reported photon AE a values for anthracene, 0.530 (8) eV; pyrene, 0.41 (1) eV; and chrysene, 0.32 (1) eV, in the NIST database . Not in the database, however, is the photon AE a value for phenanthrene of 0.12 eV .…”

“…The electron affinities of polycyclic aromatic hydrocarbons (PAHs) are important properties with reported experimental values that differ by more than the uncertainties, as observed in the subject article . These differences occur because the values have not been assigned to ground and excited states.…”