The 1 2 Σ → 1 2 ∆ transition is most promising as it involves the ground and the first excited electronic states avoiding branching to intermediate levels. The electronic density changes from a spherical distribution of the s-orbital to a clover-shaped shape of the d orbital, see Fig. . For most of the yttrium and scandium cations this transition features FCFs indicative of the expected significant vibrational branching (see Tables and in the SI). For all multiply bonded cations except for ZrS + this is one of the most diagonal transitions that we found (Tables S7-S10 in the SI).