Jeffrey P. Honovich

Threshold ion photodissociation. Bromobenzene and iodobenzene ions

Abstract Photodissociation of bromobenzene and iodobenzene ions at wavelengths near the one-photon threshold was studied as a function of pressure in an ICR ion trap. An analysis was made of the effects on the observed wavelength dependence of three factors: the thermal distribution of ion internal energies, the kinetic shift attributable to IR-radiative lifetime limiting of photoexcited ions, and the contributions of two-photon dissociation at wave-lengths near or below threshold. Quantitative procedures were developed for taking all of these into account and values were obtained for the zero-Kelvin dissociation thresholds: these are calculated to be 2.81±0.07 eV (440±10 nm) for the bromobenzene ion and 2.48±0.06 (499±12 nm) for the iodobenzene ion. A value of 1142±5 kJ mol−1 is derived for ΔHfo0(C6H5+).

Structure of benzyl chloride parent ions: An unusual bimolecular isomerization process

Abstract The benzyl chloride radical cation produced by electron ionization has been observed to undergo an isomerization reaction in the trapped source of an ion cyclotron resonance (ICR) mass spectrometer. Laser photodissociation techniques show that ionization of benzyl chloride initially produces a homogeneous population of ions absorbing in the red. These ions upon collision with benzyl chloride neutrals then react to form isomeric species absorbing in the blue. The rate constant obtained indicates a reaction collision efficiency of approximately 2% for the isomerization of red—blue-absorbing ions. This result reconciles the apparent contradictions in the literature concerning the formation of more than one structure upon ionization of benzyl chloride. Benzyl chloride has also been ionized by charge exchange to determine the effects of internal energy on the ion structures formed. It is concluded that a single initial structure (perhaps the molecular ion) results from all the ionization conditions examined.