Effect of energetic electrons on breakdown graphs determined by threshold photoelectron-photoion coincidence (TPEPICO) mass spectrometry using steradiancy analyzers

In TPEPICO mass spectrometry, a threshold photoelectron detector is employed to transmit zero kinetic energy electrons. The steradiancy analyzer normally employed allows a small but significant number of non-zero kinetic energy electrons to be transmitted as well. A method has been developed to estimate the contribution to measured breakdown graphs of energetic electrons transmitted through the detector. This technique consists of convoluting the known instrument function and the HeI photoelectron spectrum (PES) with various postulated breakdown curves until the experimental and calculated breakdown curves match. This method has been successfully applied to propane and the C₄H₈ isomers, but it cannot be applied when the HeI PES does not represent the internal energy distribution in the energy range being examined. This is the case for CF₃I; for such cases it is possible to construct a variable-energy PES if the HeI PES, the real breakdown graph and the instrument function are known.