American Chemical Society
jp4c00289_si_002.xlsx (63.74 kB)

Diabatic Valence-Hole Concept

Download (63.74 kB)
posted on 2024-04-22, 14:06 authored by Jun Jiang
A global diabatization scheme, based on the “valence-hole” concept, has been previously applied to model webs of avoided crossings that exist in four electronic-state symmetry manifolds of C2 (1Πg, 3Πg, 1Σu+, and 3Σu+). Here, this model is extended to the electronically excited states of four more molecules: CN (2Σ+), N2 (3Πu), SiC (3Π), and Si2 (3Πg). Many strangenesses in the spectroscopic observations (e.g., energy level structure, predissociation linewidths, and radiative lifetimes) for all four electronic state systems discussed here are accounted for by this unified model. The key concept of the model is valence-hole electron configurations: 3σ2142 in CN (2Σ+), 2σg2u1u4g2g1 in N2 (3Πu), 5σ2123 in SiC (3Π), and 4σg2u1g2u3 in Si2 (3Πg), all of which have a triply occupied “valence-core” (i.e., 2σg2u1 or the equivalent). These valence-hole configurations have a nominal bond order of three or higher and correlate with high-energy separated-atom limits with an np ← ns (n = 2, 3) promotion in one of the atomic constituents. On its way to dissociation, the strongly bound diabatic valence-hole state crosses multiple weakly bound or repulsive states, which belong to electron configurations with a completely filled valence-core. These curve crossings between diabatic potentials result in a network of many avoided crossings among multiple electronic states, analogous to the well-studied electronic structure landscape of ionic-covalent crossings in strongly ionic molecules. Considering the unique role of valence-hole states in shaping the global electronic structure, the valence-hole concept should be added to our intuitive framework of chemical bonding.