# Structures and Energetics of E2H3+ (E = As, Sb, and Bi) Cations

## TL;DR

This paper studies the structures and energies of E2H3+ cations (E = As, Sb, Bi) to understand their bonding and isomer stability.

## Contribution

The study reveals distinct energy minima for E2H3+ isomers and identifies the most stable structures for each element.

## Key findings

- The vinylidene-like structure is the lowest energy for As2H3+ but only a transition state for Bi2H3+.
- Trans isomers are the global minimum for Sb2H3+ and Bi2H3+.
- All minima have permanent dipole moments, suggesting observability in microwave experiments.

## Abstract

E2H2 (E = As, Sb, Bi) structures
involving
multiple bonds have attracted much attention recently. The E2H3+ cations (protonated E2H2) are predicted to be viable with substantial proton affinities
(>180 kcal/mol). Herein, the bonding characters and energetics
of
a number of E2H3+ isomers are explored
through CCSD(T) and DFT methods. For the As2H3+ system, the CCSD(T)/cc-pVQZ-PP method predicts that
the vinylidene-like structure lies lowest in energy, with the trans
and cis isomers higher by 6.7 and 9.3 kcal/mol, respectively. However,
for Sb2H3+ and Bi2H3+ systems, the trans isomer is the global minimum,
while the energies of the cis and vinylidene-like structures are higher,
respectively, by 2.0 and 2.4 kcal/mol for Sb2H3+ and 1.6 and 15.0 kcal/mol for Bi2H3+. Thus, the vinyledene-like structure is the lowest energy
for the arsenic system but only a transition state of the bismuth
system. With permanent dipole moments, all minima may be observable
in microwave experiments. Besides, we have also obtained transition
states and planar-cis structures with higher energies. The current
results should provide new insights into the various isomers and provide
a number of predictions for future experiments.