Structure and Fluxionality of B13+ Probed by Infrared Photodissociation Spectroscopy

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-B-11 isotopologue of B-13(+) 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 B-13(+) 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 B-13(+).