Absorption and electroabsorption spectra of [(NH3)(5)Ru-pyrazine](2+) and [(NH3)(5)Ru-pyrazine-H](3+) by a vibronic model Hamiltonian

The near IR-visible absorption and electroabsorption (Stark) spectra of the title compounds are studied by using a vibronic model Hamiltonian. The mod el, very simple in its electronic part, includes both bond and local (on-si te) vibrations, whose separate effects on the optical properties are also i nvestigated. We have found that bond vibrations, often neglected in model c alculations, play a significant role in the lineshape profile. Relevant mol ecular parameters, such as dipole moment and polarizability, in both the gr ound and the excited states, are computed within the framework of the prese nt model. Good agreement with the experimentally available results is found .