We use cryogenic ion vibrational spectroscopy to characterize the structure and fluxionality of the magic number boron cluster B₁₃⁺. The infrared photodissociation (IRPD) spectrum of the D₂-tagged all-¹¹B isotopologue of B₁₃⁺is reported in the spectral range from 435 to 1790 cm⁻¹and unambiguously assigned to a planar boron double wheel structure based on a comparison to simulated IR spectra of low energy isomers from density-functional-theory (DFT) computations. Born–Oppenheimer DFT molecular dynamics simulations show that B₁₃⁺exhibits internal quasi-rotation already at 100 K. Vibrational spectra derived from these simulations allow extracting the first spectroscopic evidence from the IRPD spectrum for the exceptional fluxionality of B₁₃⁺.