| Abstrakt: |
The dissociative photoionization of CH[sub 2]Br[sub 2] in a region ∼10–24 eV was investigated with photoionization mass spectroscopy using a synchrotron radiation source. An adiabatic ionization energy of 10.25 eV determined for CH[sub 2]Br[sub 2] agrees satisfactorily with predictions of 10.26 and 10.25 eV with G2 and G3 methods, respectively. Observed major fragment ions CH[sub 2]Br[sup +], CHBr[sup +], and CBr[sup +] show appearance energies at 11.22, 12.59, and 15.42 eV, respectively; minor fragment ions CHBr[sub 2][sup +], Br[sup +], and CH[sub 2][sup +] appear at 12.64, 15.31, and 16.80 eV, respectively. Energies for formation of observed fragment ions and their neutral counterparts upon ionization of CH[sub 2]Br[sub 2] are computed with G2 and G3 methods. Dissociative photoionization channels associated with six observed fragment ions are proposed based on comparison of determined appearance energies and predicted energies. An upper limit of ΔH[sub f,298][sup 0](CHBr[sup +])≤300.7±1.5 kcal mol[sup -1] is derived experimentally; the adiabatic ionization energy of CHBr is thus derived to be ≤9.17±0.23 eV. Literature values for ΔH[sub f,298][sup 0](CBr[sup +])=362.5 kcal mol[sup -1] and ionization energy of 10.43 eV for CBr are revised to be less than 332 kcal mol-1 and 9.11 eV, respectively. Also based on a new experimental ionization energy, ΔH[sub f,298][sup 0](CH[sub 2]Br[sub 2][sup +]) is revised to be 236.4±1.5 kcal mol-1. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR] |
