Variational Rice–Ramsperger–Kassel–Marcus (RRKM) theory calculations of the energy and angular momentum dependence of the rate constant for the dissociation of C6H6+ into C6H5+ and an H atom are reported. In these variational calculations both the definition of the reaction coordinate and its value are independently optimized. A model potential-energy surface which interpolates between a Morse potential at short range and an ion-induced dipole potential at long range is employed in these variational calculations. The fully optimized variational results indicate that the transition state for this dissociation occurs at separation distances of about 3–4 Å and that the available phase space in the transition state is typically a factor of 5 lower than that predicted by phase space theory. Experimental measurements were made of the time-resolved product ion intensity resulting from the laser-induced dissociation of a thermal (≊375 K) distribution of benzene cations. An ion cyclotron resonance trap was used over a range of photolysis wavelengths from 266 to 285 nm. The observed time dependences in the product ion signals are a result of both dissociative and radiative relaxation processes with a deconvolution procedure yielding estimated dissociation rate constants. Satisfactory agreement between the theoretical and experimental results, including the previous experimental results of Neusser and co-workers [J. Phys. Chem. 93, 3897 (1989), and references cited therein] is obtained for an assumed dissociation energy of 3.88 eV to the lowest triplet state of C6H5+.

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The optical absorption spectrum of gas-phase ferrocene cation was measured by photodissociation (PO) spectroscopy between 570 nm and 643 nm. The PO process was loss of a cyclopentadienyl ring from the parent cation. Some structure was observed in the PO spectrum, with the highest PO being at 603 nm. The peak spacing did not correspond to a vibrational progression in the expected totally symmetric vibrational mode, and a possible assignment of the three apparent maxima involving electronic transitions from low-lying electronic states is proposed. Information on the dissociation threshold was sought by light intensity dependence measurements at 308 nm, 266 nm, and time-resolved PD measurements at 308 nrn, 266 nrn, and 240 nm. The PD at all of these wavelengths showed two-photon characteristics, indicating that the threshold for observable one-photon PO lies higher than about 5.4 eV.