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 C-13-labeled isotopes, and weighted SERS calculations reveal the specific characteristics of these motions in the SERS signatures.