Observation of dihalide elimination upon electron attachment to oxalyl chloride and oxalyl bromide, 300-550 K.

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 Cl2(-) at all temperatures (66% at 300 K); its importance increases slightly as temperature increases. Two other product ions formed are Cl- (18% at 300 K) and the phosgene anion CCl2O- (16% at 300 K) and appear to arise from a common mechanism. With oxalyl bromide, the Br2(-) channel represents almost half of the ion product of attachment, independent of temperature. Br- accounts for the remainder. For oxalyl chloride, the attachment rate coefficient is small [(1.8 +/- 0.5) x 10(-8) cm3 s(-1) at 300 K], and increases with temperature. The attachment rate coefficient for oxalyl bromide [(1.3 +/- 0.4) x 10(-7) cm3 s(-1) at 300 K] is nearly collisional and increases only slightly with temperature. Stable parent anions C2Cl2O2(-) and C2Br2O2(-) and adduct anions Cl- (C2Cl2O2) and Br- (C2Br3O2) 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 C2Cl2O2, C2Cl2O2(-), and C2Br2O2(-), 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 C2Cl2O2 and C2Br2O2 are transition states. In contrast, the cis conformers of the anionic oxalyl halide molecules are stable, lying 131 meV above trans-C2Cl2O2(-) and 179 meV above trans-C2Br2O2(-). 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 C2Cl2O2 is "extremely flat." Our computational data indicate that the analogous torsional surfaces for C2Br2O2, C2Cl2O2(-), and C2Br2O2(-) 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.

[1]  T. Märk,et al.  Electron attachment to POCl3: measurement and theoretical analysis of rate constants and branching ratios as a function of gas pressure and temperature, electron temperature, and electron energy. , 2006, The Journal of chemical physics.

[2]  P. Karamertzanis,et al.  Molecular conformations and relative stabilities can be as demanding of the electronic structure method as intermolecular calculations. , 2006, The journal of physical chemistry. A.

[3]  L. Curtiss,et al.  Assessment of Gaussian-3 and density-functional theories on the G3/05 test set of experimental energies. , 2005, The Journal of chemical physics.

[4]  H. Schaefer,et al.  The extremely flat torsional potential energy surface of oxalyl chloride. , 2005, The Journal of chemical physics.

[5]  Niann S. Wang,et al.  Photolysis of oxalyl chloride (ClCO)2 at 193 nm: emission of CO(v, 2004, The Journal of chemical physics.

[6]  K. Hedberg,et al.  Conformational analysis. I. Molecular structure, composition, trans-gauche energy and entropy differences, and potential hindering internal rotation of gaseous oxalyl chloride as determined by electron diffraction , 2002 .

[7]  P. Španěl,et al.  Product ion distributions and rate coefficients for the attachment reactions of electrons with CHCl2Br, CCl2Br2, and CHClBr2 , 2001 .

[8]  S. Chien,et al.  Energetics and Structures of the Carbonyl Chloride Radical, Oxalyl Chloride, and Their Cations , 1999 .

[9]  J. Parnis,et al.  Gas-Phase Ion Chemistry of Oxalyl Chloride: An Electron Bombardment Matrix Isolation FTIR Spectroscopic Study , 1997 .

[10]  Daniel Chen,et al.  UV photodissociation of oxalyl chloride yields four fragments from one photon absorption , 1997 .

[11]  Wang,et al.  Generalized gradient approximation for the exchange-correlation hole of a many-electron system. , 1996, Physical review. B, Condensed matter.

[12]  P. Španěl.  AN ON-LINE LANGMUIR PROBE TECHNIQUE FOR THE STUDY OF AFTERGLOW PLASMAS , 1995 .

[13]  Jean-Philippe Blaudeau,et al.  Extension of Gaussian-2 (G2) theory to molecules containing third-row atoms K and Ca , 1995 .

[14]  T. Miller,et al.  THERMAL ELECTRON ATTACHMENT TO SF4 AND SF6 , 1994 .

[15]  P. Španěl,et al.  Studies of Electron Attachment at Thermal Energies Using the Flowing Afterglow–Langmuir Probe Technique , 1994 .

[16]  A. Becke.  Density-functional thermochemistry. III. The role of exact exchange , 1993 .

[17]  Krishnan Raghavachari,et al.  Gaussian-2 theory for molecular energies of first- and second-row compounds , 1991 .

[18]  W. B. Knighton,et al.  Effect of buffer gas and pressure variations on the formation of Br−2 in reactions of thermal electrons with dibrominated hydrocarbons and fluorocarbons , 1991 .

[19]  J. Paulson,et al.  Formation of Br−2 in the reactions of thermal electrons with some bromomethanes and bromoethanes , 1990 .

[20]  A. Allouche,et al.  Ultraviolet photoisomerizations and FT-IR investigations of matrix isolated oxalyl halide conformers , 1989 .

[21]  P. Kemper.  Gas phase ion—molecule reaction rate constants through 1986 , 1988 .

[22]  J. Mcgowan,et al.  Physics of ion-ion and electron-ion collisions. Vol. 83 , 1983 .

[23]  N. Adams,et al.  Studies of Ion-Ion Recombination using Flowing Afterglow Plasmas , 1983 .

[24]  J. Pola.  IR laser driven decomposition of oxalyl chloride in presence or radical scavengers: Evidence for molecular mechanism , 1982 .

[25]  C. Klots.  Rate constants for unimolecular decomposition at threshold , 1976 .

[26]  J. L. Franklin,et al.  Electron Affinities of the Halogen Molecules by Dissociative Electron Attachment , 1971 .