Unimolecular dissociation rates of the chlorobenzene cation prepared by multiphoton ionization

Abstract

We have studied the unimolecular reaction C 6 H 5 CI+-+C6H5+ + CI as a function of internal energy by using multi photon ionization (MPI) on a supersonically cooled jet of chlorobenzene to prepare the excited parent ion. Specific rate constants k (E) were obtained from an analysis of the distorted C6HS+ peak shape in a time-of-flight (TOF) mass spectrometer. Decomposition in the wavelength region 265-270 nm is shown to proceed by two-photon ionization followed by onephoton absorption. The internal energy of the excited parent ion is characterized in a separate experiment which measures the photoelectron kinetic energy distribution, obtained over the same wavelength range. The specific rate constants found in this study compare well with previous literature values, thus validating this MPI TOF technique for the determination of ion decomposition rates.

Specific Rate Constants k(E) of the Dissociation of the Halobenzene Ions: Analysis by Statistical Unimolecular Rate Theories

“…These rate constants, which extend between 2-3 orders of magnitude, agree well with the current data. In 1984, Durant et al 27 used a supersonically cooled sample of chlorobenzene Comparison of current experimental data with previously reported data. SSACM curves are calculated using the parameters that best describe the data presented in this paper.…”

Photoelectron Photoion Coincidence Studies of Ion Dissociation Dynamics

“…Aside from benzene and its deuterated analogues, 50 " 52 the rates of only aniline, 47 chlorobenzene, 48,49 and phenetole 46 ions have been reported. One of the difficulties lies in finding molecules that can be energy selected with the available lasers in any given laboratory.…”

“…67 These dissociation reactions have been investigated by many workers with different techniques. 48,49,61,68 ' 72 Dannacher et al? * investigated the I atom loss from iodobenzene with particular care.…”

Metastable Dissociation of Anions Formed by Electron Attachment

“…[1][2][3] Particularly valuable information is obtained if the total excess energy E* of the metastable complex is known, for example by selectively exciting specific states in multiphoton ionization experiments. [4][5][6] However, for large molecular ions energy selection is rarely achieved. In studies of cations formed from neutral precursors by photon or electron impact, a major obstacle is the unknown amount of energy that is carried away by the electrons, though this can be overcome with the photoelectron-photoion coincidence method.…”