The dissociation energies and dissociation dynamics of iodoacetonitrile (ICH2CN) have been investigated by the photoelectron photoion coincidence (PEPICO) spectroscopy technique. The 0 K onsets for the following products were determined: +CH2CN + I-. (12.188 +/- 0.005 eV) and (CH2CN)-C-. + I+ (12.345 +/- 0.010 eV). From the difference between these two values the ionization energy of the (CH2CN)-C-. was found to be 10.294 + 0.010 eV. By using a thermodynamic cycle that involves the gas phase acidity of CH3CN, the election affinity of the (CH2CN)-C-. radical, and an accurate heat of formation of acetonitrile, a Delta(f)H degrees(298)(ICP2CN) of 172.5 +/-4.0 kJ mol(-1) is derived. This latter value is considerably higher than the best theoretical value of 153 kJ mol(-1).