Unimolecular and Photoinduced Dissociations of Aromatic C8H10+• Molecular Ions

Abstract

Production of C7H7+ in the unimolecular and photoinduced dissociations of ethylbenzene; methylcycloheptatriene; and o-, m-, and p-xylene ions has been investigated using mass-analyzed ion kinetic energy spectrometry. Both the benzylium and tropylium ions were produced near the reaction threshold, whereas only the benzylium ion was observed at higher internal energy achieved by photoabsorption. Experimental data suggest that interconversion between ethylbenzene and methylcycloheptatriene ions occurs more rapidly than their dissociations near the reaction threshold, whereas xylene ions undergo rate-determining isomerization to the methylcycloheptatriene structure, and dissociation occurs from the ethylbenzene/methylcycloheptatriene ion mixture. The processes occurring at higher internal energy are quite similar, except that the tropylium channel cannot compete against the benzylium channel because either the ethylbenzene ion-to-methylcycloheptatriene ion conversion or the dissociation of the methylcyclohept...