Electron affinities and C60 anion clusters of certain bowl-shaped polycyclic aromatic hydrocarbons

Abstract

The kinetic method is applied to the determination of the electron affinities (EAs) of the bowl-shaped polycyclic aromatic hydrocarbons (PAHs) dibenzo[a,g]corannulene (C28H14) 1 and diindenochrysene (C26H12) 2 using electron attachment desorption chemical ionization mass spectrometry (DCI-MS) and triple-quadrupole tandem mass spectrometry. The estimated EAs of 1 and 2 are 1.00±0.20 and 1.16±0.20 eV respectively. In an analogous experiment, loosely bound dimeric radical anions comprising C60 with 1 and C60 with 2 were generated in the gas phase by electron attachment desorption chemical ionization. The collision-induced dissociation of each of these cluster ions yields both the monomeric radical anions as products and yields calculated electron affinities of C60 of 1.20±0.20 eV (C60/1 dimer) and 1.24±0.20 eV (C60/2 dimer). These values are significantly different from the known electron affinity of C60 (2.65 eV) and support previous studies on electron-bound dimers comprising C6O and coronene [G. Chen, R. G. Cooks, E. Corpuz and L. T. Scott, J. Am. Soc. Mass Spectrom. 7, 619 (1996)] in showing that the dissociation of electron-bound dimers comprising C60 and reference PAHs is controlled by the electron affinity of a portion of the C60 surface, i.e. that a ‘local’ electron affinity of C60 is measured. The ‘local’ electron affinity value corresponds approximately to the electron affinity of the reference PAHs, C60 exhibiting an affinity for the ‘extra’ electron in the cluster which approximately matches that of its PAH partner. © 1997 by John Wiley & Sons, Ltd.