MASS-SPECTROMETRIC AND THEORETICAL DETERMINATION OF POLYNUCLEAR AROMATIC HYDROCARBON PROTON AFFINITIES

Proton affinities (PAs) in the gas phase have been calculated for a se ries of polynuclear aromatic hydrocarbons by MOPAC 6.0 using AM1 and P M3 Hamiltonians and compared to the experimental values published in t he literature, A correlation between PAs and the reactional competitio n leading to the respective formation of the molecular ion and the pro tonated molecular ion under ammonia positive-ion chemical ionization ( PICI) has been demonstrated. A method for estimating PAs from ion abun dances in the ammonia PICI mass spectra is proposed.