Archive for June 2nd, 2021

A closer look at that fourth bond in C2.

Wednesday, June 2nd, 2021

From the last few posts here, you might have noticed much discussion about how the element carbon might sustain a quadruple bond. The original post on this topic from some years ago showed the molecular orbitals of the species CN+, which included two bonding π-types and a low lying nodeless bonding σ-orbital, all with double occupancies and adding up to a triple bond. Discussing now C2 itself, there are two remaining orbitals for consideration which we will for the purpose here call the highest occupied σ-MO or HOσMO (Σu) and the lowest unoccupied σ-MO or LUσMO (Σg) and which are more mysterious.