Some Ions of High Kinetic Energy in Mass Spectra of Polyatomic Molecules

Abstract

When the lighter‐fragment ions of hydrocarbons and hydrocarbon derivatives are recorded with low‐ion accelerating voltages, one observes satellite peaks on the high‐mass side of the main peaks that come from ions with a fairly homogeneous high kinetic energy. Observations of the satellite peaks of CH₃⁺ ions in mass spectra of 13 hydrocarbons and CH₃CF₃, are reported. The kinetic energies range from 1.5 to 3.4 ev and the relative intensities have a wide range of values but are less than the main peak except in benzene. The appearance potential of the satellite peak is roughly 30 volts in most cases while the main peak is observed above 20 volts. These high‐energy ions are ascribed to doubly charged molecule ions that dissociate into two singly charged fragments. The kinetic energy of the pair of fragment ions is in most cases nearly equal to the Coulomb energy of two ions at a distance equal to the greatest distance between valence electrons in the molecule.