Ionization Energies of ClO and Cl2O2

The ionization energies of chlorine oxide (ClO) and its dimer (Cl2O2) have been measured using monochromatic synchrotron radiation in the 10−20 eV energy regime in combination with photoionization mass spectrometry. The threshold energy of ClO+ (m/z = 51) is found at 10.85 ± 0.05 eV, whereas the ionization threshold of Cl2O2+ (m/z = 102) occurs at 11.05 ± 0.05 eV. The experimental values are compared to results from ab initio calculations, where three stable isomers of Cl2O2 are considered:  dichlorine peroxide (ClOOCl), chloryl chloride (ClClO2), and chlorine chlorite (ClOClO). The results indicate that the experimental threshold energy of Cl2O2+ is due to adiabatic ionization of ClOOCl. T…