| Abstract
| - Polycyclic aromatic hydrocarbon (PAH) molecules undergo facile ionization in cryogenic water-ices resultingin near quantitative conversions of neutral molecules to the corresponding singly charged radical cations.Here we report, for the first time, the production and stabilization of a doubly ionized, closed shell PAH inwater-ice. The large PAH quaterrylene (QTR, C40H20) is readily photoionized and stabilized as QTR2+ in awater-ice matrix at 20 K. The kinetic analysis of photolysis shows that the QTR2+ is formed at the expenseof QTR+, not directly from QTR. The long-axis polarized S1−S0 (1B3u ← 11Ag) transition for QTR2+ fallsat 1.59 eV (782 nm). TD-DFT calculations at the B3LYP level predict that this transition falls at 1.85 eV(670 nm) for free gas-phase QTR2+, within the 0.3 eV uncertainty associated with these calculations. Thisred shift of 0.26 eV is quite similar to the 0.24 eV red shift between the TD-DFT computational predictionfor the lowest energy transition for QTR+ (1.68 eV) and its value in a water matrix (1.44 eV). These resultssuggest that multiple photoionization of such large PAHs in water-ice can be an efficient process in general.
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