Investigation of linear and nonlinear Raman scattering for isotopologues of Ru(bpy) ₃ 2⁺

Tris(2,2′-bipyridine)ruthenium(II), Rubpy, an important transition metal complex for its robust photochemistry, is studied using simulated resonance Raman scattering (RRS) and resonance hyper-Raman scattering (RHRS) in comparison to measured surface-enhanced Raman scattering (SERS) and surface-enhanced hyper-Raman scattering (SEHRS). Detailed examination of the simulated data shows that many of the observed features in the experiments are captured by the theory. For the metal-to-ligand charge transfer (MLCT) absorption band at 452 nm, it is demonstrated that the shoulder on the absorption band at 425 nm is not a vibronic feature and that the line shape should be considered as coming from two separate MLCT states. We find that good agreement can be obtained by comparing simulated spectra to the SERS and SEHRS spectra on resonance with the absorption band. However, the simulations do not capture the high sensitivity of relative peak intensities observed during wavelength scanned SERS and SEHRS experiments. This result is interpreted on the basis of discussion of the literature and the approximations made in the vibronic model, where it is concluded that the simulations underestimate interference effects. These results demonstrate the complexity of using theoretical methods for accurately describing the electronic structure of large molecules, and that commonly used exchange-correlation functionals like B3LYP and LC-PBE cannot completely describe all of the vibronic features in the Raman scattering of Rubpy.