Scalar relativistic and spin-orbit effects in closed-shell superheavy-element monohydrides

Abstract

Relativistic and electron correlation effects are investigated for the closed-shell superheavy-element monohydrides RgH, $112{\text{H}}^{+}$, 113H, $114{\text{H}}^{+}$, 117H, $118{\text{H}}^{+}$, 119H, and $120{\text{H}}^{+}$. Periodic trends are discussed by comparing the calculated properties to the ones for the lighter elements. The size of the relativistic effects varies considerably between the different molecules with the $s$-block elements being dominated by scalar relativistic effects and the $p$-block elements dominated by spin-orbit effects. In most cases, relativistic effects are more important than electron correlation effects and both are nonadditive as one expects. $120{\text{H}}^{+}$ behaves in a counterintuitive way as it shows a relativistic bond-length expansion together with a large relativistic decrease in the dissociation energy. The reason behind this anomalous behavior is due to the relativistically diminished valence-$7d$ participation in the 120-H bond.