A full-dimensional quantum dynamics study of the photodetachment of HCO2- is reported using an exact wavepacket method. The calculated photodetachment spectrum identified several HCO2 resonances observed in the experiment, but with quantitatively different intensities, indicating imperfection in the HCO2 potential-energy surface. The narrow widths of the lowest resonances indicate slow tunneling-facilitated predissociation. The dissociation of these resonances yields CO2 not only in its ground vibrational state, but also in excited ones, particularly at high energies. Both the symmetric stretching and bending modes, which are coupled via Fermi resonance, are found to be excited. (C) 2011 Elsevier B. V. All rights reserved.