HEAT OF FORMATION AND ADIABATIC ELECTRON-AFFINITY OF NH2

A pulsed ion cyclotron resonance spectrometer has been employed to determine the proton affinity of NH2· and the acidity of NH3. The measured proton affinity of NH2·, 186.5 ± 2 kcal mol-1, combined with the ionization potential of NH3 yields a homolytic bond dissociation energy for ammonia of 107.1 ± 2.2 kcal mol-1. This bond energy has been used, along with the heats of formation of NH3 and H·, to calculate a heat of formation of NH2· of 44.0 ± 2.3 kcal mol-1. Combining the proton affinity of NH2· with the measured acidity of ammonia, 403.1 ± 1 kcal mol-1, and the molecule's ionization potential, yields a value of 17.6 ± 3.2 kcal mol-1 for the electron affinity of the amino free radical. Several examples of ion cyclotron double resonance results are given, and their interpretation is discussed. © 1979 American Chemical Society.