Doubly charged ion spectra in mass spectra of hydrocarbons

A compilation of doubly charged ions in the mass spectra of 148 hydrocarbons has been made, based on mass spectra published in the American Petrole um Institute Catalog of Mass Spectral Data. In hydrocarbons with three, four, or five carbon atoms, the most probable double ionization process involves loss of all but two or three hydrogen atoms without breaking carbon bonds. Unsaturated molecules give larger doubly charged ion peaks t han saturated molecules, and ions with an even number of hydrogen atoms tend to be more abundant than those with an odd number. In saturated hydrocarbons with six or more carbon atoms, double ionization with breaking of carbon bonds is most probable, but in benzenes and highly unsaturated molecules, double ionization without loss of carbon atoms is probable. These heavier molecules show di stinctive differences depending on molecular structure.