Appearance energies of singly, doubly, and triply charged coronene and corannulene ions produced by electron impact

Electron impact ionization near threshold has been studied for the polyaromatic hydrocarbons coronene and corannulene using a high resolution electron monochromator in conjunction with quadrupole mass spectrometry. The mass spectra determined at an electron energy of 100 eV show a rich fragmentation pattern (particularly for coronene) including the presence of multiply charged molecular cations for both compounds. For the singly and multiply charged parent ions of coronene and corannulene we present the ionization efficiency curves near threshold from which the corresponding appearance energies (AEs) are determined using a nonlinear least squares fitting routine. The AEs obtained here are compared where available with previous values reported for both compounds using electron impact ionization and photoionization as well as with theoretical predictions.