Trapping a Photoelectron Behind a Repulsive Coulomb Barrier in Solution.

Multiply charged anions (MCAs) display unique photophysics and solvent-stabilizing effects. Well-known aqueous species such as SO42- and PO43- experience spontaneous electron detachment or charge-separation fragmentation in the gas phase owing to the strong Coulomb repulsion arising from the excess of negative charge. Thus, anions often present low photodetachment thresholds and the ability to quickly eject electrons into the solvent via charge-transfer-to-solvent (CTTS) states. Here, we report spectroscopic evidence for the existence of a repulsive Coulomb barrier (RCB) that blocks the ejection of "CTTS-like" electrons of the aqueous B12F122- dianion. Our spectroscopic experimental and theoretical studies indicate that despite the exerted Coulomb repulsion by the nascent radical monoanion B12F12aq-center dot, the photoexcited electron remains about the B12F12-center dot core. The RCB is an established feature of the potential energy landscape of MCAs in vacuo, which seems to extend to the liquid phase highlighting recent observations about the dielectric behavior of confined water.