Stimulated Raman pumping of C2− probed via resonant two-photon detachment

We demonstrate for the first time that stimulated Raman pumping (SRP) can be used to vibrationally excite gas-phase negative ions. Results are presented for C2−, in which stimulated Raman pumping excites a rotationally resolved transition between the ν = 0 and ν = 1 levels of the ground 2Σg+ state; this excitation is monitored by resonant two-photon detachment through the excited B 2Σu+ state. At least 35% conversion to the ν = 1 level was achieved in this study. It is expected that this method is quite generally applicable and will provide an excellent tool for the study of the vibrational spectroscopy of negative ions.