TIME-RESOLVED PHOTODISSOCIATION OF 3 TERT-BUTYLBENZENE IONS

Time-resolved photodissociation (TRPD) in the ion cyclotron resonance ion trap was used to observe the slow dissociation of tri-tert-butylbenzene ion at four wavelengths between 615 and 532 nm. Dissociation rates of the order of 5 x 10(3) to 3 x 10(4) s-1 were found for thermalized ions. An excellent fit to the observed curves was obtained by convoluting an RRKM rate-energy curve with the thermal distribution of ion internal energies at 375 K. RRKM parameters for the best fit were E0 = 1.2 +/- 0.1 eV and DELTA-S double-ended-dagger = -7 +/- 7 cal K-1. Although this is the largest ion for which energy-resolved dissociation kinetic data have been obtained, there was no indication of a breakdown in the quasiequilibrium theory description of the dissociation. For tert-butylbenzene ion and di-tert-butylbenzene ions, dissociation at visible wavelengths was found to be fast on the TRPD time scale (5 x 10(5) s-1).