Benzene Radical Anion Microsolvated in Ammonia Clusters: Modelling the Transition from an Unbound Resonance to a Bound Species

TL;DR

This study models how benzene radical anion transitions from a metastable resonance in gas phase to a stable, solvated species in ammonia clusters, revealing the solvation process's role in stabilization.

Contribution

It introduces a computational approach combining DFT with auxiliary methods to study solvation effects on the benzene radical anion in clusters of increasing size.

Findings

Cluster size dependence of binding energy converges at -2.3 eV.

Solvation stabilizes the radical anion from a resonance to a bound state.

Methodology reduces computational cost for large systems.

Abstract

The benzene radical anion, well-known in organic chemistry as the first intermediate in the Birch reduction of benzene in liquid ammonia, exhibits intriguing properties from the point of view of quantum chemistry. Notably, it has the character of a metastable shape resonance in the gas phase, while measurements in solution find it to be experimentally detectable and stable. In this light, our previous calculations performed in bulk liquid ammonia explicitly reveal that solvation leads to stabilization. Here, we focus on the transition of the benzene radical anion from an unstable gas-phase ion to a fully solvated bound species by explicit ionization calculations of the radical anion solvated in molecular clusters of increasing size. The computational cost of the largest systems is mitigated by combining density functional theory with auxiliary methods including effective fragment potentials or approximating the bulk by polarizable continuum models. Using this methodology, we obtain the cluster size dependence of the vertical binding energy of the benzene radical anion converging to the value of $-$2.3 eV at a modest computational cost.