A comparison of ground- and excited-state properties of gas phase and crystalline ruthenocene using density functional theory

The ground- and excited-state properties of both gas phase and crystalline ruthenocene, ${\mathrm{Ru(cp)}}_{\mathrm{2}},$ are investigated using density functional theory. A symmetry-based technique is employed to calculate the energies of the multiplet splittings of the singly excited triplet states. For the crystalline system, a Buckingham potential is introduced to describe the intermolecular interactions between a given ${\mathrm{Ru(cp)}}_{\mathrm{2}}$ molecule and its first shell of neighbors. The overall agreement between experimental and calculated ground- and excited-state properties is very good as far as absolute transition energies, the Stokes shift and the geometry of the excited states are concerned. An additional energy lowering in the ${}^3{B}_2$ component of the ${\text{5a}}_1^{\prime }{\text{→4e}}_1^{″}$ excited state is obtained when the pseudolinear geometry of ${\mathrm{Ru(cp)}}_{\mathrm{2}}$ is relaxed along the low-frequency bending vibration.