Genuine Molecular Effects in Bound-State Quantum Electrodynamics

Quantum electrodynamics (QED) currently features prominently at the precision frontier in describing the structure of atoms and molecules. Dominant QED effects are governed by the electronic structure in the vicinity of the nucleus and are therefore generally regarded as atomic in origin, with molecular contributions largely arising from additive atomic contributions. By studying the nuclear magnetic resonance shielding tensors of thallium in Tl$X$, we reveal genuinely molecular QED effects that strongly depend on the bonding partner ($X$ = F, Cl, Br, I, At) and are absent in the Tl${}^{+}$ ion.