Breakdown of the singlet and triplet nature of electronic states of the superheavy element 114 dihydride (114H2)

It is demonstrated that the superheavy element (114) forms a dihydride with electronic features that exhibit breakdown of the conventional singlet (X¹A₁) and triplet (³B₁) states due to large relativistic effects including spin-orbit effects. The ¹A₁ state is shown to undergo avoided crossing with the ³B₁(A₁) state and other states in the C2v2 double group. We have carried out relativistic complete active-space multiconfiguration interaction followed by multireference configuration interaction computations including spin-orbit effects that included several million configurations including 6d electron correlations for the electronic states of the superheavy element (114)H₂. The potential energy curves of both ground and excited states are computed including electron correlation and spin-orbit effects simultaneously. The curves exhibit unusual features from their traditional nonrelativistic counterparts: namely, ¹A₁, ³B₁, and ¹B₁ states due to spin-orbit coupling. The spin-orbit effects are shown to destabilize (114)H₂ by almost 2.6 eV.