Dissociation of State-Selected Ions Studied by Fixed-Photon-Energy Double-Imaging Photoelectron Photoion Coincidence: Cases of O₂⁺ and CH₃F⁺

This study presents the method of fixed-photon-energy double-imaging photoelectron photoion coincidence (i2PEPICO) utilized to investigate the dissociation of state-selected ions. Vacuum ultraviolet (VUV) synchrotron radiation at one fixed photon energy of hν = 21.2 eV, the He(I) atomic resonance energy, is employed as a light source to ionize molecules. Various dynamic information including time-of-flight (TOF) mass spectra, mass-selected photoelectron spectra (PES), and electron and ion kinetic energy correlation diagrams corresponding to each mass are obtained efficiently with the multiplexed capabilities of i2PEPICO, thereby revealing the detailed dissociation mechanisms of ions. As representative examples, dissociation of state-selected O2+ ions prepared in the b4∑g− and B2∑g− electronic states and CH3F+ ions in the X2E, A2A1, and B2E states were selected and investigated