Butterfly, Vinylidene‐Like, Monobridged and Trans Structures of Si₂H₂⁺: Comparison to the Well‐Characterized Neutral Si₂H₂

Abstract This paper investigates four of the constitutional isomers of Si 2 H 2 + , namely the butterfly, vinylidene‐like, monobridged, and trans structures. These isomer geometries were all studied using the CCSD(T) method with basis sets as large as cc‐pV5Z. Higher level methods CCSDT and CCSDT(Q) were used for final energetics. It is found that the butterfly isomer has the lowest energy, followed by vinylidene‐like and monobridged structures; the trans structure has the highest energy of the four. All structures were compared with their neutral counterparts. Partial charges are computed and it is found that all isomers share the positive charge between the silicon atoms. NBO analysis shows that the cation Si−Si bond order is reduced by 0.5 relative to the neutral versions of the same isomer in the case of the butterfly, vinylidene‐like, and monobridged; and reduced by 0.6 for the trans isomer. Vibrational frequencies, infrared intensities, and dipole moments are predicted to encourage the spectroscopic identification of Si 2 H 2 + .