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

Abstract

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.