AVS 49th International Symposium
    Surface Science Tuesday Sessions
       Session SS2-TuA

Paper SS2-TuA4
Chemical Reactions Induced by Ionizing and Electron-beam Irradiation in Organohalide/Water (Ice) Films

Tuesday, November 5, 2002, 3:00 pm, Room C-110

Session: Atmospheric Surface Chemistry
Presenter: C.C. Perry, Johns Hopkins University
Authors: C.C. Perry, Johns Hopkins University
N.S. Faradzhev, Rutgers, The State University of New Jersey
A.J. Wagner, Johns Hopkins University
C. Vecitis, Johns Hopkins University
G. Wolfe, Johns Hopkins University
D.H. Fairborther, Johns Hopkins University
T.E. Madey, Rutgers, The State University of New Jersey
Correspondent: Click to Email
We report on the reactions of organohalides (CCl@sub 4@, CHCl@sub 3@, CH@sub 2@Cl@sub 2@, PhCl, CF@sub 2@Cl@sub 2@) in water (ice) films (~50 nm) at ~100K under the influence of ionizing and electron beam irradiation using reflection-absorption infrared spectroscopy, X-ray photoelectron spectroscopy and mass spectrometry. The final neutral gas phase products of electron-stimulated degradation of chlorocarbons CCl@sub 4@, CHCl@sub 3@, CH@sub 2@Cl@sub 2@, and PhCl, were identified as CO@sub 2@, CO, and HCl. Product species identified in the film include a thermally stable partially chlorinated (C@sub x@Cl@sub y@) overlayer, CO@sub 2@, H@sub 3@O@super +@ and Cl@super -@. Phosgene (COCl@sub 2@) was also observed except in the case of PhCl. For CCl@sub 4@/H@sub 2@O mixtures, the product branching distributions are sensitive to the film@super '@s initial H@sub 2@O/CCl@sub 4@ composition. In CCl@sub 4@ rich films, the dominant reaction products in the film were C@sub 2@Cl@sub 4@ and the C@sub x@Cl@sub y@ overlayer; CO was the dominant gas phase species. In H@sub 2@O rich films, CO@sub 2@ becomes dominant at the expense of C@sub 2@Cl@sub 4@ and C@sub x@Cl@sub y@ species. For films concentrated with CCl@sub 4@ chlorine is lost principally into the gas phase while in water rich films chlorine is partitioned principally as HCl, producing H@sub 3@O@super +@ and Cl@super -@. In contrast, Freon-12 (CF@sub 2@Cl@sub 2@) / water mixtures subject to e-beam or X-ray irradiation produced carbonyl fluoride (COF@sub 2@), a major source of fluorine in the stratosphere. H@sub 3@O@super +@ and CO@sub 2@ were also detected as stable reaction products as well as Cl@super -@ and F@super -@, consistent with a recent study of negative ion yields in ESD from CF@sub 2@Cl@sub 2@/water films. The decomposition rate of different organohalides in ice film under electron beam irradiation varied dramatically (~100): Freon being much more sensitive to electron exposure than the chlorocarbons.