New and Unusual Bonding in Open Shell van der Waals Molecules Revealed by the Heavy Atom Effect:  The Case of BAr

Abstract

Calculations are reported for the excited 1 4 Π and C 2 ∆ electronic states of BAr and the (nominally 2s2p 2 ) 4 P and 2 D states of atomic boron. It was found necessary to extend an augmented valence triple-zeta orbital basis set to correctly describe the C 2 ∆ state. This enhancement is necessitated by the near degeneracy of the valence 2s2p 2 2 D and Rydberg 2s 2 3d 2 D electron configurations in atomic boron, both of which are required to describe BAr C 2 ∆. Unexpectedly strong bonding in the C 2 ∆ state is found. This bonding is shown to have its root in a type of coordinate covalency, dative bonding, that is sensitive to electron correlation effects and is reflected in a large external heavy atom effect in the spin-orbit coupling of the 1 4 Π and C 2 ∆ states.

On the strongly bound B 3Π state of the CAr van der Waals complex: Bonding and predissociation

“…As this type of dative interaction is sensitive to the level of correlation it was termed correlation sensitive dative bonding. 2 This stabilization due to the interaction of the empty (C 2sp ) orbital and the doubly occupied (Ar 3p z ) orbital is consistent with the increase in the importance of electron configuration ͑3c͒ in the B 3 ⌸ state with decreasing R. Table I Fig. 5.…”

“…Similar behavior was seen in the strongly bound 2 ⌬ state of BAr. 2 The unifying feature in CAr(B 3 ⌸) and BAr( 2 ⌬) is an empty (M 2sp ) orbitals, MϭB,C, a partially 2s2 p z hybridized M orbital, that can delocalize the electrons in the highest occupied rare gas (Rg pz ) orbital. As this type of dative interaction is sensitive to the level of correlation it was termed correlation sensitive dative bonding.…”

On the origin of the heavy atom effect in the fine-structure splitting of the 1 2Π state of alkali metal P2-rare gas van der Waals molecules

“…At the AS2-SOCI/B2 level the 1 2 ⌸ state in LiNe is unbound. This point has been previously discussed with regard to the C 2 ⌬ state of BAr, 19 and will be further explored in a future work dealing with bonding in BNe complexes. 20 In the current context the most important conclusion from these figures is that although the bonding described by E 1 2 ⌸ (R) is quite sensitive to the level of treatment, A so (R) is virtually independent of the level of treatment.…”

“…The under-estimation of D e for LiAr is symptomatic of the well known difficulty of describing argon containing van der Waal complexes. 19,22 In the computations of A so , potential energy curves inferred from spectral data will be used. Table II presents tion constructed from the experimentally determined spectroscopic constants, R e , e , and e x e presented in Ref.…”

Potential energy curves and spin-orbit coupling of light alkali-heavy rare gas molecules

“…Such a variation with the distance is comparable to the variation observed for the (1 4 ,C 2 ) SO coupling of the BAr molecule. 37 The R dependence of both coefficients reflects the differential occupation of the outer RG p shell with spin-up (α) and spin-down (β) electrons. In the quadrupole field of the excited 2 P state of the alkali atom, the RG atom is polarized.…”