Appearance Potentials of Some Metastable Transition Ions Found in Hydrocarbon Mass Spectra

The appearance potentials of some metastable transition peaks in normal butane, isobutane, the butenes, and 1,3-butadiene have been studied along with the parent ions in each metastable transition. A comparison shows that in most cases studied, an additional energy of about 2 ev is required for the formation of the metastable state. However, in the case of normal butane, two transitions were studied in which no additional energy was required within an experimental error of 0.3 ev. Evidence is presented which indicates that in some cases the appearance potentials of ions in hydrocarbon spectra are affected by these metastable ion contributions. This effect may account for some of the unexplained discrepancies found in published data on hydrocarbon gases. Check values of some ions in methane, ethane, and propane were taken to determine the performance of the instrument. A comparison of these results is made with previously published data.