A Photoelectron−Photoion Coincidence Study of the ICH₂CN Ion Dissociation:  Thermochemistry of ^•CH₂CN, ⁺CH₂CN, and ICH₂CN

Abstract

The dissociation energies and dissociation dynamics of iodoacetonitrile (ICH 2 CN) have been investigated by the photoelectron photoion coincidence (PEPICO) spectroscopy technique. The 0 K onsets for the following products were determined: + CH 2 CN + I • (12.188 ± 0.005 eV) and • CH 2 CN + I + (12.345 ± 0.010 eV). From the difference between these two values the ionization energy of the • CH 2 CN was found to be 10.294 ± 0.010 eV. By using a thermodynamic cycle that involves the gas phase acidity of CH 3 CN, the electron affinity of the • CH 2 CN radical, and an accurate heat of formation of acetonitrile, a Δ f H ° 298 (ICH 2 CN) 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 .