First-principles characterisation of spectroscopic and bonding properties of cationic bismuth carbide clusters

Vibrational and electronic absorption spectra calculated at the (time-dependent) density functional theory level for the bismuth carbide clusters BinC2n+ (3⩽n⩽9) indicate significant differences in types of bonding that depend on cluster geometry. Analysis of the electronic charge densities of these clusters highlighted bonding trends in these complex open-shell systems consistent with the spectroscopic information. The data indicate that larger clusters (n>5) have significant non-covalent bonding character and are likely to be kinetically unstable, in agreement with the cluster mass distribution obtained in gas-aggregation source experiments. The spectral fingerprints of the different clusters obtained from our calculations also suggest that identification of specific BinC2n+ structural isomers should be possible based on infra-red and optical absorption spectroscopy.