Abstract: The spectroscopy and dynamics of molecular excited states are important for the understanding of molecular electronic structures and the interactions among the electronic motion, nuclear vibration and molecular rotation. We have set up an IR-IR double optical resonance experimental apparatus to study the perturbation facilitated two photon resonance in alkaline dimers. Using an XUV laser and zero kinetic energy photoelectron spectroscopy we have studied the spectroscopy of various important molecular ions, such as the electronic-vibrational interaction in CH3CN+/CD3CN+ （the Jahn-Teller effect）.