Molecular Photodetachment Microscopy

The photodetachment microscopy technique, which was originally used with atomic negative ions, is now applied to a molecular anion. The interferograms of several rotational thresholds corresponding to transitions from OH^- X ¹Σ⁺ $v=0$ states to OH X ²Π3/2,1/2 $v=0$ states have been recorded. No effect due to the 1/r² dipolar potential of the neutral molecule appears. Using a double-pass scheme of the laser on the negative ion beam, we measure the energy of the first few detachment thresholds with improved accuracy. The new recommended value of the electron affinity of ¹⁶OH is 14 740.996(13) cm^-1, or 1.827 650 3(17) eV.