Effect of overcrowding on mass spectra of aromatic hydrocarbons

Abstract

Mass spectra of condensed polycyclic aromatic hydrocarbons with or without overcrowding, which have three, four, five, and nine fused aromatic rings, were examined. Their patterns reflect the type of overcrowding and the number of overcrowded hydrogen atoms in the molecule. These facts were supported by the ionization efficiency curves and especially the lowering of appearance energies of the [M– 2]ⁱ⁺ ions of benzo[c]phenanthrene and dibenzo[c,g]phenanthrene or the [M– 4]ⁱ⁺ ions of tetrabenzo[a,cd,j,lm]perylene.