PHOTODISSOCIATION OF GAS-PHASE POLYCYLIC AROMATIC HYDROCARBON CATIONS

The photostablities of two dozen polycyclic aromatic hydrocarbon (PAH) cations and a fullerene, C-60(+), have been tested. The molecular rad ical cations have been produced by both electron impact and laser deso rption, then trapped and mass-analyzed in a Fourier transform ion cycl otron resonance mass spectrometer, The PAH cations were subjected to v isible and UV radiation (lambda greater than or equal to 185 nm) from a Xe are lamp. Fragmentation patterns fall into four groups: photostab le, hydrogen loss only, hydrogen and carbon loss, and photodestroyed. The fragmentation patterns are discussed with respect to prior experim ental and theoretical models. Implications of these findings for the ' 'PAH hypothesis'' and the unidentified interstellar infrared (UIR) emi ssion bands are discussed briefly.