High-Resolution Photoelectron Spectroscopy of Vibrationally Excited OH.

The effect of vibrational pre-excitation of anions on their photoelectron spectra is explored, combining slow photoelectron velocity-map imaging of cryogenically cooled anions (cryo-SEVI) with tunable IR radiation to pre-excite the anions. This new IR cryo-SEVI method is applied to OH- as a test system, where the R(0) transition of the hydroxyl anion (3591.53 cm-1) is pumped. Vibrational excitation induces a 30% depletion in photodetachment signal from the v = 0, J = 0 ground state of the anion and the appearance of all five allowed, rotationally resolved photodetachment transitions from the OH- (v = 1, J = 1) level, each with peak widths between 1 and 2 cm-1. By scanning the IR laser, IR cryo-SEVI can also serve as a novel action technique to obtain the vibrational spectrum of OH-, giving an experimental value for the R(0) transition of 3591(1.2) cm-1.