Photoionization efficiency spectrum and ionization energy of C₂H₅SO

The photoionization efficiency (PIE) spectrum of C₂H₅SO was measured in the spectral range 110-150 nm by means of a photoionization mass spectrometer coupled to a synchrotron radiation source. C₂H₅SO radicals were generated by reacting O atoms with C₂H₅SC₂H₅ or C₂H₅SSC₂H₅ in a discharge flow tube. The ionization energy of C₂H₅SO was determined to be (8.71±0.02) eV, in agreement with theoretical calculations of 8.8 eV for ionization from C₂H₅SO to singlet C₂H₅SO ⁺ using the G2 method. PIE spectrum also shows a sharp increase at 10.0 eV, corresponding to the ionization energy from C₂H₅SO to triplet C_2H5SO ⁺ predicted by theory. Theoretical calculations also predict two stable conformers with similar energies for each of C₂H₅SO, singlet C₂H₅SO ⁺, and triplet C₂H₅SO ⁺, respectively; these conformers are indistinguishable in our experiments.