Electron tunneling through the repulsive Coulomb barrier in photodetachment of multiply charged anions

There exists a repulsive Coulomb barrier for electrons in multiply charged anions. Tunneling through this barrier is expected to be important in photodetachment of MCAs. Photodetachment spectra were found to shift to lower binding energies in the tunneling regime. We present a systematic study of the tunneling effect in photodetachment experiments on a series of dianions, −O2C(CH2)nCO2− (n=3–6). The observed tunneling effect and spectral shift are explained using WKB approximation based on a model potential with a square well at short range and a repulsive Coulomb potential at long range.