Fragmentation of valence electronic states of CF⁺₄ and SF⁺₆ studied by threshold photoelectron-photoion coincidence spectroscopy

Abstract

Threshold photoelectron-photoion coincidence (TPEPICO) spectroscopy has been used to measure, state selectively, the decay pathways of all the valence states of CF⁺₄ and SF⁺₆ in the range 15–28 eV. Radiation in the vacuum UV from a synchrotron radiation source ionises the parent molecule, and the electrons and ions are detected by threshold electron analysis and time-of-flight mass spectroscopy, respectively. TPEPICO spectra are recorded continuously as a function of photon energy, allowing both threshold photoelectron spectra and yields of all the fragment ions to be obtained. Kinetic energy releases are measured at fixed photon energies with good time resolution. The results orf the $\text{X}$²T₁, $\text{A}$²T₂ and $\text{B}$²E states of CF⁺₄ (all below the energy of He I radiation) confirm earlier measurements; results for the $\text{C}$²T₂ and $\text{D}$²A₁ states at 21.7 and 25.1 eV, respectively, are new. They confirm previous measurements that radiative decay from both states is an important process, and we have measured their state-selected fluorescence quantum yields. For SF⁺₆, fluorescence does not occur from any of the excited valence states, and we have measured the fragmentation channels and branching ratios for all of the valence states.