IONIZATION-ENERGY DETERMINATION BY THE KINETIC METHOD

Ionization energies of organic compounds can be determined by the kine tic method by dissociation of radical cations of van der Waals complex es. The ionized dimeric complexes of benzene and substituted benzenes, generated in the ion source of a multiquadrupole instrument by gentle charge exchange chemical ionization using carbon disulfide as reagent gas, when mass-selected and allowed to undergo collision-induced diss ociation with argon, yield only the two individual radical cations as products. The logarithm of the ratio of their ion abundances correlate s linearly with their ionization energies. Using this linear relations hip, the ionization energy of 3-iodobenzonitrile was determined to be 9.39 +/- 0.05 eV, and this case serves to illustrate the application o f the kinetic method in the determination of an unknown ionization ene rgy. From the slope of the kinetic method plot, it is evident that the clusters are weakly bound (effective temperature, 1670 K). Strengths of this method are the simplicity of the procedure and its potential a pplication to a wide variety of compounds.