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−1 and 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+.
A molecular ball bearing: The first spectroscopic evidence for the exceptional fluxionality of the magic number boron cluster B13+ is presented. The vibrational spectrum of D2‐tagged 11B13+ is reported and assigned to a planar boron double‐wheel structures based on a comparison to results from density‐functional‐theory computations. The spectral fingerprint of internal quasi‐rotation is identified with the aid of molecular dynamics simulations.