Observation of dihalide elimination upon electron attachment to oxalyl chloride and oxalyl bromide, 300-550 K
- Department of Chemistry, College of the Holy Cross, Worcester, Massachusetts 01610-2395 (United States)
Rate coefficients have been measured for electron attachment to oxalyl chloride [ClC(O)C(O)Cl] and oxalyl bromide [BrC(O)C(O)Br] in He gas at 133 Pa pressure over the temperature range of 300-550 K. With oxalyl chloride, the major ion product of attachment is Cl{sub 2}{sup -} at all temperatures (66% at 300 K); its importance increases slightly as temperature increases. Two other product ions formed are Cl{sup -} (18% at 300 K) and the phosgene anion CCl{sub 2}O{sup -} (16% at 300 K) and appear to arise from a common mechanism. With oxalyl bromide, the Br{sub 2}{sup -} channel represents almost half of the ion product of attachment, independent of temperature. Br{sup -} accounts for the remainder. For oxalyl chloride, the attachment rate coefficient is small [(1.8{+-}0.5)x10{sup -8} cm{sup 3} s{sup -1} at 300 K], and increases with temperature. The attachment rate coefficient for oxalyl bromide [(1.3{+-}0.4)x10{sup -7} cm{sup 3} s{sup -1} at 300 K] is nearly collisional and increases only slightly with temperature. Stable parent anions C{sub 2}Cl{sub 2}O{sub 2}{sup -} and C{sub 2}Br{sub 2}O{sub 2}{sup -} and adduct anions Cl{sup -}(C{sub 2}Cl{sub 2}O{sub 2}) and Br{sup -}(C{sub 2}Br{sub 3}O{sub 2}) were observed but are not primary attachment products. G2 and G3 theories were applied to determine geometries of products and energetics of the electron attachment and ion-molecule reactions studied. Electron attachment to both oxalyl halide molecules leads to a shorter C-C bond and longer C-Cl bond in the anions formed. Trans and gauche conformers of the neutral and anionic oxalyl halide species have similar energies and are more stable than the cis conformer, which lies 100-200 meV higher in energy. For C{sub 2}Cl{sub 2}O{sub 2}, C{sub 2}Cl{sub 2}O{sub 2}{sup -}, and C{sub 2}Br{sub 2}O{sub 2}{sup -}, the trans conformer is the most stable conformation. The calculations are ambiguous as to the oxalyl bromide geometry (trans or gauche), the result depending on the theoretical method and basis set. The cis conformers for C{sub 2}Cl{sub 2}O{sub 2} and C{sub 2}Br{sub 2}O{sub 2} are transition states. In contrast, the cis conformers of the anionic oxalyl halide molecules are stable, lying 131 meV above trans-C{sub 2}Cl{sub 2}O{sub 2}{sup -} and 179 meV above trans-C{sub 2}Br{sub 2}O{sub 2}{sup -}. Chien et al. [J. Phys. Chem. A 103, 7918 (1999)] and Kim et al. [J. Chem. Phys. 122, 234313 (2005)] found that the potential energy surface for rotation about the C-C bond in C{sub 2}Cl{sub 2}O{sub 2} is ''extremely flat.'' Our computational data indicate that the analogous torsional surfaces for C{sub 2}Br{sub 2}O{sub 2}, C{sub 2}Cl{sub 2}O{sub 2}{sup -}, and C{sub 2}Br{sub 2}O{sub 2}{sup -} are similarly flat. The electron affinity of oxalyl chloride, oxalyl bromide, and phosgene were calculated to be 1.91 eV (G3), and 2.00 eV (G2), and 1.17 eV (G3), respectively.
- OSTI ID:
- 20783278
- Journal Information:
- Journal of Chemical Physics, Vol. 124, Issue 18; Other Information: DOI: 10.1063/1.2196409; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
AFFINITY
ANIONS
BROMINE IONS
CHLORINE IONS
ELECTRON ATTACHMENT
EV RANGE 01-10
ION-MOLECULE COLLISIONS
MEV RANGE 100-1000
ORGANIC BROMINE COMPOUNDS
ORGANIC CHLORINE COMPOUNDS
OXALATES
PHOSGENE
REACTION KINETICS
TEMPERATURE RANGE 0273-0400 K
TEMPERATURE RANGE 0400-1000 K