Photoionization mass spectrometry of chlorine oxides

Abstract Photoionization mass spectrometry of four chlorine oxides (Cl 2 O, Cl 2 O 4 , Cl 2 O 6 , and Cl 2 O 7 ) is reported. Photoionization efficiency curves of parent and fragment ions are measured in the energy regime between 10 and 21 eV using monochromatic synchrotron radiation. Ionization energies (IE) of the chlorine oxides and fragmentation appearance energies (AE) are obtained from photoion yield curves of mass-selected cations. Specifically, we obtain IE(Cl 2 O) = 10.88 ± 0.02 eV, IE(Cl 2 O 4 ) = 11.23 ± 0.05 eV, IE(Cl 2 O 6 ) = 12.66 ± 0.05 eV, and IE(Cl 2 O 7 ) = 12.15 ± 0.05 eV. The experimental results are used to derive numerous thermochemical stability data of the neutral and ionic chlorine oxides and their fragments, as well as plausible cation fragmentation mechanisms. Resonant excitation with tunable vacuum ultraviolet radiation is applied in the case of Cl 2 O to obtain further insight into autoionization processes. Three series of Rydberg excitations are assigned converging to the C ( 2 A 2 ) ionization energy at 12.74 eV.