Trapping a Photoelectron behind a Repulsive Coulomb Barrier in Solution

Area of Science:

• Physical Chemistry
• Chemical Physics
• Spectroscopy

Background:

• Multiply charged anions (MCAs) exhibit unique photophysics and solvent interactions.
• Aqueous MCAs like SO4(2-) and PO4(3-) often undergo electron detachment or fragmentation in the gas phase due to Coulomb repulsion.
• Anions typically have low photodetachment thresholds and can eject electrons into solvents via charge-transfer-to-solvent (CTTS) states.

Purpose of the Study:

• To investigate the photophysics of the aqueous B12F12(2-) dianion.
• To provide spectroscopic evidence for a repulsive Coulomb barrier (RCB) in aqueous MCAs.
• To understand the behavior of photoexcited electrons in multiply charged anions in solution.

Main Methods:

• Spectroscopic experiments were conducted on the aqueous B12F12(2-) dianion.
• Theoretical studies were performed to analyze the potential energy landscape.
• Ultrafast electron dynamics were probed to observe electron ejection behavior.

Main Results:

• Spectroscopic evidence confirmed the existence of an RCB for the aqueous B12F12(2-) dianion.
• The RCB was found to block the ejection of "CTTS-like" electrons.
• Experimental and theoretical data showed that the photoexcited electron remains localized near the B12F12(-•) core, despite Coulomb repulsion.

Conclusions:

• The repulsive Coulomb barrier (RCB) is not limited to the gas phase but extends to the liquid phase for aqueous MCAs.
• This RCB phenomenon influences the dielectric behavior of confined water.
• The findings challenge the typical understanding of electron ejection from anions in solution.