Highly variable carbon environment in the κ-(BEDT-TTF)2Cu2(CN)3 salt probed by carbon K-edge x-ray absorption and resonant inelastic x-ray scattering spectroscopy

Using near-edge x-ray absorption fine structure (NEXAFS) and resonant inelastic x-ray scattering (RIXS) at the C K-edge, we have studied the carbon environment and dynamics in kappa-(BEDT-TTF)2Cu2(CN)3 and supplemented them by density functional theory calculations. The maximum in the NEXAFS pre-edge is identified to originate mainly from nonequivalent carbon sites of the BEDT-TTF molecule, whereas the anionic carbons contribute to the intensity at higher energy. RIXS spectra show resonant reinforcement of the interorbital excitations, but without a clear set of vibrational harmonics, previously detected in our N K-edge RIXS study. This finding points to the strong multimode vibrational excitation of all carbon sites in both (BEDT-TTF)2+ molecular and Cu2(CN)3- anionic subsystems, thus demonstrating a strongly disordered environment which might have important implications for the electronic state of the kappa-(BEDT-TTF)2Cu2(CN)3.