Structures and Energetics of E 2 H 3 + (E = As, Sb, and Bi) Cations.

E 2 H 2 (E = As, Sb, Bi) structures involving multiple bonds have attracted much attention recently. The E 2 H 3 + cations (protonated E 2 H 2 ) are predicted to be viable with substantial proton affinities (>180 kcal/mol). Herein, the bonding characters and energetics of a number of E 2 H 3 + isomers are explored through CCSD(T) and DFT methods. For the As 2 H 3 + 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 Sb 2 H 3 + and Bi 2 H 3 + 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 Sb 2 H 3 + and 1.6 and 15.0 kcal/mol for Bi 2 H 3 + . 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.