Experimental and theoretical studies of the benzylium(+)/tropylium(+) ratios after charge transfer to ethylbenzene

Abstract

Benzylium versus tropylium ion yields from the fragmentation of ethylbenzene cations at various excitation energies are studied by forming excited ethylbenzene cations by charge transfer from a series of charge-transfer agents and by identifying the benzylium ion by its secondary reaction with neutral ethylbenzene. At lower excitation energies, the tropylium ion yield decreases with increasing energy from values near 16% (at an energy of 230 kJ mol(-1)) to 5% (at an energy of 500 kJ mol(-1)). At higher excitation energies, the tropylium ion yield increases again, which is attributed to secondary isomerization of the vibrationally highly excited benzylium ion arising from the primary fragmentation. It is suggested that this isomerization competes with radiative cooling of the excited benzylium ion. The experimental observations are rationalized in the framework of statistical unimolecular rate theory and electronic structure calculations.