Hydrogen atom elimination from polycyclic aromatic hydrocarbons with sustained off-resonance irradiation: a new approach to produce carbon/hydrogen cluster cations C nH x+

Abstract

The stepwise elimination of hydrogen atoms from nine polycyclic aromatic hydrocarbons (PAHs) was investigated by the collision-induced dissociation of the sustained off-resonance irradiation (SORI-CID) technique of Fourier transform ion cyclotron resonance mass spectrometry. In every case the application of sequential SORI-CID resulted in the predominant loss of a single hydrogen atom from the parent ions, and for coronene, perylene, and benz[a]anthracene, this eventually produced pure carbon cluster ions C n ·+. No carbon cluster ions were observed for small PAHs because of competing fragmentations or insufficient intensities of the parent ions. As a common feature of the larger polycyclic aromatic hydrocarbons studied, hydrogenated carbon cluster ions C n H 5 + were produced smoothly after elimination of five hydrogen atoms (from pyrene, C 16H 10, and fluorene, C 13H 10) or of seven hydrogen atoms (from coronene, C 24H 12, perylene, C 20H 12, benz[a]anthracene, C 18H 12, chrysene, C 18H 12, and triphenylene, C 18H 12). However, uncomplicated further loss of hydrogen atoms to produce cluster ions C n H 4 ·+ (or C n H 3 +) was observed only for benz[a]anthracene, chrysene, and triphenylene. The different dissociations of C n H x + with odd and even numbers of hydrogen atoms and the difficulty to form C n H x + (0 ≤ x ≤ 4) by multisteps of single hydrogen elimination are discussed. The latter observation may be attributed to characteristically different structures of hydrogenated carbon cluster ions C n H x + with x ≥ 5 and x ≤ 4.