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 κ-(BEDT-TTF)2Cu2(CN)3 and supplemented them by density functional theory (DFT) calculations. The maximum in the NEXAFS pre-edge is identified to originate mainly from non-equivalent 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 inter-orbital excitations, but without clear set of vibrational harmonics, detected previously in our N K-edge RIXS study. This finding points to the strong multi-mode 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 κ-(BEDT-TTF)2Cu2(CN)3.
