Vibrational Mode Assignment of Diisopropyl Benzimidazolium N-Heterocyclic Carbenes on Gold

Raman, surface-enhanced Raman, and infrared vibrational spectra of diisopropyl benzimidazolium N-heterocyclic carbenes were experimentally measured and calculated using first-principles theory. Experimental data were in excellent agreement with the theory and allowed for assignment of previously unreported vibrational modes in the molecule. Key vibrational motions of the Au–C bond, benzene ring, and isopropyl wingtips were isolated using 13C-labeled isotopes, and weighted SERS calculations reveal the specific characteristics of these motions in the SERS signatures.