Fig. 1: Mass spectra and mass defect of iodine oxides.

a Time-of-flight mass spectrum (ToF-MS) at photoionization energy (PIE) of 10.5 eV (10 Torr, [O₃] = 2 × 10¹⁵ molecule cm⁻³, no added H₂O) averaged over 20 ms after the photolysis laser pulse. Two sections of the spectrum are displayed with an offset and multiplied by 40 and 100 to show more clearly the peaks corresponding to higher m/z clusters. For the third section (red), the corresponding pre-photolysis background is also shown. The asterisks indicate groups of peaks with even number of iodine atoms. ToF-MS signal in arbitrary units. b Mass-defect plot (the difference between molecular mass and the integer mass given by the sum of protons and neutrons in the nuclei) for the main clusters observed. The area of the dots is proportional to the corresponding log-scaled signal intensity. Peak progressions in steps of I₂O₅ units can be distinguished, but a substantial I₂O₅⁺ signal (x symbol) is absent both at 10.5 eV and 11.6 eV. The blue squares indicate the O/I ratio of the main peaks at the right-hand-side axis (uncertainties are smaller than symbol sizes). The empty square with error bar shows the O/I ratio measured elsewhere for iodine oxide particles (IOPs)²⁶. c In blue, the difference between spectra with and without water (10.5 eV, 4 Torr, [O₃] = 4 × 10¹⁴ molecule cm⁻³). Negative peaks indicate losses and positive peaks formation of the corresponding species. Sections of the spectra with and without water are shown (black and red lines, respectively), multiplied by 10 for clarity.