Second Differential Ionization-Efficiency Curves for Fragment Ions by Electron Impact

A study has been made of the information obtainable from second-differential ionization-efficiency curves for fragment ions produced by electron impact. To aid in the interpretation of the appearance-potential data, measurements were made of the kinetic energy of the fragment ions. From the second-differential electron-impact curves, it is shown that accurate appearance potentials of many fragment ions cannot be obtained by orthodox methods, e.g., CH3+(C2H6). For a few fragment ions such as CH3+(CH4), it is possible to obtain a valid appearance potential. The main result of the kinetic-energy retardation studies is that few fragment ions appear to have kinetic energy for electron ionizing energies near to the fragment-ion appearance potential.