Loss Of Cl Atom Research Articles

Reactive pathways in the bromobenzene-ammonia dimer cation radical: Evidence for a roaming halogen radical

Photoinitiated reactions in van der Waals complexes provide a means to examine reactive pathways from well-defined initial geometries. In recent work, we re-examined reactive pathways following resonant two-photon ionization (R2PI) of the chlorobenzene-ammonia (PhCl⋯NH3) dimer. The dimer cation radical reacts primarily via Cl atom loss, and additional channels corresponding to HCl and H atom loss were identified. The structure of the reactive complex was confirmed as an in-plane σ-type, and computational studies of the dimer cation radical potential energy landscape revealed two nearly isoenergetic arenium ion intermediates (or Wheland intermediates). The intermediate produced from ipso addition was not stable with respect to either Cl or HCl loss, and the relative branching observed in experiment was well reproduced by microcanonical transition state theory (TST) calculations. Here, we report experimental and computational studies of the related PhBr⋯NH3 dimer, examined for the first time. We present evidence that the dimer structure is also an in-plane σ-type. However, in contrast to the PhCl⋯NH3 system, calculations predict that the structure of the reactive intermediate corresponds to a distonic ion-radical complex, where the radical density is largely localized on the bromine atom. The calculated barrier to HBr loss is sufficiently high to render this channel nearly insignificant (less than 1% branching) in TST calculations, yet experiment shows a sizable (37%) branching into this channel. We rationalize these results in terms of a roaming Br radical mechanism for HBr formation.

Reactive Pathways in the Chlorobenzene–Ammonia Dimer Cation Radical: New Insights from Experiment and Theory

Building upon our recent studies of noncovalent interactions in chlorobenzene and bromobenzene clusters, in this work we focus on interactions of chlorobenzene (PhCl) with a prototypical N atom donor, ammonia (NH3). Thus, we have obtained electronic spectra of PhCl···(NH3)n (n = 1-3) complexes in the region of the PhCl monomer S0 -S1 (ππ*) transition using resonant 2-photon ionization (R2PI) methods combined with time-of-flight mass analysis. Consistent with previous studies, we find that upon ionization the PhCl···NH3 dimer cation radical reacts primarily via Cl atom loss. A second channel, HCl loss, is identified for the first time in R2PI studies of the 1:1 complex, and a third channel, H atom loss, is identified for the first time. While prior studies have assumed the dominance of a π-type complex, we find that the reactive complex corresponds instead to an in-plane σ-type complex. This is supported by electronic structure calculations using density functional theory and post-Hartree-Fock methods and Franck-Condon analysis. The reactive pathways in this system were extensively characterized computationally, and consistent with results from previous calculations, we find two nearly isoenergetic arenium ions (Wheland intermediates; denoted WH1, WH2), which lie energetically below the initially formed dimer cation radical complex. At the energy of our experiment, intermediate WH1, produced from ipso-addition, is not stable with respect to Cl or HCl loss, and the relative branching between these channels observed in our experiment is well reproduced by microcanonical transition state theory calculations based upon the calculated parameters. Intermediate WH2, where NH3 adds ortho to the halogen, decomposes over a large barrier via H atom loss to form protonated o-chloroaniline. This channel is not open at the (2-photon) energy of our experiments, and it is suggested that photodissociation of a long-lived (i.e., several ns) WH2 intermediate leads to the observed products.

Deactivation mechanism of AuCl3 catalyst in acetylene hydrochlorination reaction: a DFT study

The deactivation mechanism of AuCl3 catalyst in the reaction of acetylene hydrochlorination was studied by using AuCl3 dimer model and the density functional theory (DFT) method. Four possible paths for the acetylene hydrochlorination reaction catalyzed by AuCl3 were illustrated with corresponding transition states. The activation free energies and reaction rate constants of the four paths were also analyzed. It is apparent that when HCl and C2H2 coadsorbed on the AuCl3 dimer, the C2H2 was co-catalyzed by HCl and the AuCl3 dimer to produce C2H3Cl and the reaction energy barrier was as low as 23.35 kcal mol−1. If the HCl in the gas phase could not adsorb on the Au site within the set time, the intermediate chlorovinyl was difficult to desorb from the AuCl3 catalyst as its desorption energy was as high as 41.336 kcal mol−1. As the reaction temperature increased, C2H2 became easier to be adsorbed on the AuCl3 catalyst prior to HCl, which resulted in the side reaction and the rapid deactivation of the AuCl3 dimer due to the loss of Cl atoms. Our calculations are necessary for us to clearly understand the experimental results, which indicate a great dependence of activity and stability of AuCl3 catalysts on the HCl : C2H2 ratio as well as the temperature.

Understanding the Complex Dissociation Dynamics of Energy Selected Dichloroethylene Ions: Neutral Isomerization Energies and Heats of Formation by Imaging Photoelectron−Photoion Coincidence

The dissociative photoionization of 1,1-C(2)H(2)Cl(2), (E)-1,2-C(2)H(2)Cl(2), and (Z)-1,2-C(2)H(2)Cl(2) has been investigated at high energy and mass resolution using the imaging photoelectron photoion coincidence instrument at the Swiss Light Source. The asymmetric Cl-atom loss ion time-of-flight distributions were fitted to obtain the dissociation rates in the 10(3) s(-1) < k < 10(7) s(-1) range as a function of the ion internal energy. The results, supported by ab initio calculations, show that all three ions dissociate to the same C(2v) symmetry ClC═CH(2)(+) product ion. The 0 K onset energies thus establish the relative heats of formation of the neutral isomers, that is, the isomerization energies. The experimental rate constants, k(E), as well as ab initio calculations indicate an early isomerization transition state and no overall reverse barrier to dissociation. The major high energy channels are the parallel HCl loss and the sequential ClC═CH(2)(+) → HCCH(+) + Cl process, the latter in competition with a ClC═CH(2)(+) → ClCCH(+) + H reaction. A parallel C(2)H(2)Cl(2)(+) → C(2)HCl(2)(+) + H channel also weakly asserts itself. The 0 K onset energy for the sequential Cl loss reaction suggests no barrier to the production of the most stable acetylene ion product; thus the sequential Cl-atom loss is preceded by a ClC═CH(2)(+) → HC(Cl)CH(+) reorganization step with a barrier lower than that of the second Cl-atom loss. The breakdown diagram corresponding to this sequential dissociation reveals the internal energy distribution of the first C(2)H(2)Cl(+) daughter ion, which is determined by the kinetic energy release in the first, Cl loss reaction at high excess energies. At low kinetic energy release, this distribution corresponds to the predicted two translational degrees of freedom, whereas at higher energies, the excess energy partitioning is characteristic of only one translational degree of freedom. New Δ(f)H(o)(298K) of 3.7, 2.5, and 0.2 ± 1.75 kJ mol(-1) are proposed for 1,1-C(2)H(2)Cl(2), (E)-1,2-C(2)H(2)Cl(2), and (Z)-1,2-C(2)H(2)Cl(2), respectively, and the proton affinity of ClCCH is found to be 708.6 ± 2.5 kJ mol(-1).

The low pressure Cl2/O2 discharge and the role of ClO

A global (volume averaged) model is applied to a low pressure (1–100 mTorr) high density chlorine discharge that is diluted with oxygen. The influence of oxygen dilution on the particle densities and the electron temperature is explored. The electronegativity is found to increase strongly with increased pressure in a chlorine-rich mixture, whereas it is nearly pressure independent in an oxygen-rich mixture. The chlorine dissociation fraction increases with increased oxygen dilution, although the increase is neither pronounced nor sharp at low oxygen content. We explore the role of the ClO molecule in the discharge and confirm that the ClO molecule is mainly created through recombination of Cl and O atoms at the chamber wall, which in turn significantly increases the loss of Cl atoms in oxygen-rich mixtures. The most important loss process for ClO is electron impact dissociation in the plasma bulk. The molecular ion ClO+ is almost entirely created by charge transfer for oxygen dilution below 67%, while electron impact ionization becomes the dominant creation process for ClO+ at higher dilution.

Detection of Binuclear Copper—Caffeine Complexes under Electrospray Ionization Condition

A number of copper salts, Cu(OOCCH(3))(2), Cu(ClO(4))(2), Cu(NO(3))(2), CuCl(2) and CuSO(4) have been tested for their ability to form binuclear copper-caffeine complexes. The electrospray ionization (ESI) mass spectra of methanol solution containing caffeine and CuCl(2) or CuSO(4) show signals of two copper atom containing ions, so the signals correspond to binuclear complexes: [2Caf + Cu(2)SO(4)](+), [2Caf + Cu(2)](+), [2Caf + Cu(2)Cl](+), [2Caf + Cu(2)Cl(2)](+) and [2Caf + Cu(2)Cl(3)](+). Sulfate and chloride anion are characterized by charge densities higher than those of the carboxylate, nitrate and perchlorate anion. Thus, due to the electrostatic forces, the binuclear complexes containing SO(4)(2-) or Cl(-) can survive the transfer from solution to the gas phase and then can successfully be observed on ESI mass spectra. The ion [2Caf + Cu(2)Cl(3)](+) is present in solution and could be detected when using methanol/chloroform as solvent. The ions [2Caf + Cu(2)](+), [2Caf + Cu(2)Cl](+) and [2Caf + Cu(2)Cl(2)](+) are formed from the [2Caf + Cu(2)Cl(3)](+) ion (by subsequent loss of Cl atoms) on transfer from the solution to the gas phase or in the gas phase. The ion [2Caf + Cu(2)](+) does not contain a bridging agent, thus it is reasonable to assume that it contains a Cu-Cu bond.

Influence of the reactor wall composition on radicals’ densities and total pressure in Cl2 inductively coupled plasmas: II. During silicon etching

In an industrial inductively coupled plasma reactor dedicated to silicon etching in chlorine-based chemistry, the density of Cl2 molecules and the gas temperature are measured by means of laser absorption techniques, the density of SiClx (x⩽2) radicals by broadband absorption spectroscopy, the density of SiCl4 and ions by mass spectrometry, and the total gas pressure with a capacitance gauge. These measurements permit us to estimate the mole fractions of Cl, SiCl4, and etch product radicals when etching a 200mm diameter silicon wafer. The pure Cl2 plasma is operated in well prepared chamber wall coating with a thin film of SiOCl, AlF, CCl, or TiOCl. The impact of the chemical nature of the reactor wall’s coatings on these mole fractions is studied systematically. We show that the reactor wall coatings have a huge influence on the radicals densities, but this is not only from the difference on Cl–Cl recombination coefficient on different surfaces. During silicon etching, SiClx radicals sticking on the reactor walls are etched by Cl atoms and recycled into the plasma by forming volatile SiCl4. Hence, the loss of Cl atoms in etching the wall deposited silicon is at least as important as their wall recombination in controlling the Cl atoms density. Furthermore, because SiCl4 is produced at high rate by both the wafer and reactor walls, it is the predominant etching product in the gas phase. However, the percentage of redeposited silicon that can be recycled into the plasma depends on the amount of oxygen present in the plasma: O atoms produced by etching the quartz roof window fix Si on the reactor walls by forming a SiOCl deposit. Hence, the higher the O density is, the lower the SiCl4 density will be, because silicon is pumped by the reactor walls and the SiOCl layer formed is not isotropically etched by chlorine. As a result, in the same pure Cl2 plasma at 20mTorr, the SiClx mole fraction can vary from 18% in a SiOCl-coated reactor, where the O density is the highest, to 62% in a carbon-coated reactor, where there is no O. In the latter case, most of the Cl mass injected in the reactor is stored in SiCl4 molecules, which results in a low silicon etch rate. In this condition, the Cl mass balance is verified within 10%, and from the silicon mass balance we concluded that SiClx radicals have a high surface loss probability. The impact of the reactor wall coating on the etching process is thus important, but the mechanisms by which the walls control the plasma chemistry is much more complicated than a simple control through recombination reaction of halogen atoms on these surfaces.

The gas-phase thermochemistry of PCl 4+: A test of lattice energy calculations

The bond dissociation energy for loss of Cl atom from PCl 4 + has been measured to be 411 ± 17 kJ mol −1 at 0 K using energy-resolved collision-induced dissociation in a flowing afterglow-guided ion beam tandem mass spectrometer. Density functional calculations give bond energies that are lower than experiment, while MP2 calculations are in good agreement. The bond energy can be combined with the ionization energy of PCl 3 to derive the 0 K heat of formation of PCl 4 +, 378 ± 18 kJ mol −1. This value is in good agreement with the value derived from lattice energy calculations.

Electrospray mass spectrometry of cis-[Ru(NO)Cl(bpy)2]2+ (bpy=2,2′-bipyridine): fragmentation from desolvated {[Ru(NO)Cl(bpy)2]2+, Cl−}+ ion pairs by electron transfer and internal Lewis base pathways

The electrospray mass spectrum (ESI-MS) of cis-[Ru(NO)Cl(bpy)2]Cl2 (bpy=2,2′-bipyridine), obtained from 50% CH3OH/50% H2O as the mobile solvent, exhibited ruthenium-containing ions derived from a {[RuII(NO+)Cl(bpy)2]2+, Cl−}+ ion pair (m/z=514) and [RuII(NO+)Cl(bpy)2]2+ (m/z=239.5). [RuIIICl(bpy)2]2+, from the loss of NO from the 239.5 ion, is detected at m/z=224.5. Only the m/z 514 ion pair is detected when 100% CH3OH mobile solvent is used, but the presence of even small amounts of water prompted the additional detection of the m/z 239.5 and m/z 224.5 ions under tandem MS–MS conditions. Ruthenium-chloro-containing ions appear as a characteristic collection of eight main, and four lesser, intense ions created from combinations 104Ru, 102Ru, 101Ru, 99Ru, 98Ru, 96Ru, 35Cl and 37Cl isotopes with minor contributions from 13C, etc. For convenience of discussion, only the most abundant m/z species are mentioned herein as representative of all the isotopically distributed ions.Four fragmentation channels are detectable from the m/z=514 chloride ion pair: (1) the loss of HCl (main channel; ca. 50% of fragmentation events), (2) the loss of NO (ca. 12% ), (3) the loss of bpy (minor pathway), and (4) the loss of Cl atom (ca. 38% ).Loss of NO from ion m/z 514 yields ion m/z 484, which is the precursor of ions m/z 448 (by loss of HCl), m/z 328 (by loss of bpy) and m/z 292 (by loss of HCl and bpy). Loss of HCl from ion m/z 514 generates ion m/z 478, [RuII(NO+)Cl(bpyH)(bpy-H)]+, deprotonated at the ortho C–H of one bpy ligand. In MS–MS experiments, the m/z 478 ion was established to undergo loss of NO, producing ion m/z 448, rejoining further fragmentation process for ion m/z 448 at this point. Loss of neutral bipyridine from m/z 514 in low yield produces ion m/z 358, which undergoes further loss of NO to form [RuCl2(bpy)]+ ion (m/z=328). MS–MS “neutral loss of 30” spectra confirmed the NO loss events as part of the fragmentation sequence for all four pathways.A fourth species of m/z=479 from the “514” ion is obtained by an internal electron transfer from Cl− of the ion pair, and loss of the resultant neutral Cl atom. The product [RuII(NO·)Cl(bpy)2]+ “479” fragment undergoes facile loss of NO to generate [RuIICl(bpy)2]+ (m/z=449). Ion m/z 449 gives rise to ions m/z 413 (loss of HCl) and m/z 257(loss of HCl and bpy). MS–MS experiments confirm the neutral loss of Cl from the m/z 514 ion, and the formation of the m/z 449 ion via m/z 479 and m/z 514 parents. This pathway was not observed in a prior study for the related complex, [Ru(NO)Cl(dpaH)(dpa−)]+ (dpaH=2,2′-dipyridylamine), which does not have an external Cl− in an ion pair.

Catalytic isomerization of 1-hexene to 2-hexene by halide clusters of Nb, Mo, Ta and W possessing an octahedral metal core

Halide clusters, [(M 6Cl 12)Cl 2(H 2O) 4]·4H 2O (M: Nb, Ta) and (H 3O) 2[(M 6Cl 8)Cl 6]·6H 2O (M: Mo, W) with an octahedral metal framework, develop catalytic activity for the isomerization and slight hydrogenation of olefinic double bonds when the halide clusters are treated in a stream of hydrogen at elevated temperatures. In the case of Nb clusters, treatment above 200 °C produces the catalytic activity. Raman spectra of such heat-treated clusters show that the cage breathing motion of Nb 6 remains intact, whereas the breathing vibrations of the edge bridging Nb–Cl of [Nb 6Cl 12] disappear. In the case of W clusters, the catalytic activity appears at 300 °C, at which temperature the structure of [(W 6Cl 8)Cl 4(H 2O) 2] begins to decay to form W 6Cl 12. Maximum activity emerges at 450 °C, at which temperature the structure of W 6Cl 12 begins to decay. Elemental analyses of both clusters show the loss of Cl atoms. Thus, activation of these clusters occurs by partial loss of the halogen ligands, leaving the cluster framework intact.

Modeling kinetic shifts in threshold collision-induced dissociation. Case study: Dichlorobenzene cation dissociation

A threshold collision-induced dissociation (CID) study is performed on dichlorobenzene cation dissociation of both the ortho and para isomers. Ab initio calculations are performed on the system to investigate the details of the potential energy surface with respect to Cl atom loss and to provide the molecular parameters necessary for CID cross section modeling. The effects of kinetic shifts on the CID threshold determinations are investigated using a model that incorporates statistical unimolecular decay theory. The model is tested using unimolecular dissociation rate constants as a function of energy provided by earlier photoelectron–photoion-coincidence (PEPICO) experiments. The different possible sets of parameters involved in the CID model, their effect on the dissociation rates, and their effect on the final CID threshold determination are discussed. A tight transition state is observed to reproduce the experimental dissociation rates better than a phase-space limit loose transition state, a result attributed to a potential energy surface that is much more attractive than a simple ion-induced dipole potential. The dissociation thresholds derived from CID data are in reasonable agreement with the ones derived from fitting the PEPICO rates when similar transition state assumptions are used. A final analysis of the CID data yields 0 K dissociation energies for the Cl atom loss from dichlorobenzene of 3.22±0.17 eV for the ortho isomer and 3.32±0.18 eV for the para isomer. In the present study we support a mechanism that the dissociations of the two isomers proceed through a direct bond cleavage, rather than through isomerization to a common intermediate.

Branching ratios for competing channels in the reaction of HOCO radicals with NO

The yields of CO2 from the reactions of HOCO radicals with O2 and with NO have been compared using the technique of time-resolved infrared absorption. In two separate series of experiments, HOCO radicals have been generated by (i) broadband ultraviolet photolysis of acrylic acid (CH2CHCOOH) and (ii) the reaction, Cl + HCOOH → HCl + HOCO, following pulsed laser photolysis of Cl2 at 351 nm. In the latter experiments, the observed CO2 yields were corrected for the loss of Cl atoms by the reactions Cl + NO + He → ClNO + He and Cl + ClNO → Cl2 + NO. Our measurements on the rate of Cl + NO + He yield a value of the third-order rate constant of (5.1 ± 0.7) × 10−32 cm6 molecule−2 s−1. The results of the main experiments show that the yield of CO2 from the reaction between NO + HOCO is appreciably less than that from O2 + HOCO and is dependent on the total pressure in the range 10 to 100 Torr. We interpret this as showing that the reactions HOCO + NO → HNO + CO2 and HOCO + NO(+M) → HOC(O)NO(+M) occur at similar rates, with the latter reaction being favoured at the higher total pressure.

HCFC-31: the CHClFO 2 + NO → CHClFO + NO 2 reaction and Cl atom elimination from CHClFO

The kinetics and mechanism of the reaction of CHClFO 2 radicals with NO were studied by time-resolved mass spectrometric monitoring of the molecular ions of NO 2 and NO. The rate constant was determined to be (1.31 ± 0.20) × 10 −11 cm 3 molecule −1 s −1 at (26 ± 1)°C, and was found to be independent of pressure over the range 6–25 Torr. The CHClFO radicals formed in this reaction were found to dissociate by unimolecular CCl bond scission. The unimolecular rate coefficient for Cl atom loss was estimated to be greater than 3 × 10 3 s −1 at (26 ± 1)°C.

228.8 nm Photolysis of 1,1,1-trichloroethane

Room temperature photolysis of up to 100 Torr of 1,1,1-trichloroethane in the presence of iodine at 228.8 nm, and 30 Torr 1,1,1-trichloroethane, also in the presence of iodine, and with added CF 4 was investigated. The main photodecomposition pathways are molecular elimination of HCl and CCl bond scission, with Φ HCl/Φ CCl approximately equal to 3 at low pressure. The yields of CCl 2CH 2 formed by HCl elimination decrease with increasing pressure, while the products of radical reactions resulting from CCl dissociation are independent of pressure. The results are consistent with Cl atom loss occurring from the σ* state populated by 228.8 nm photoexcitation, while HCl elimination does not occur from either σ* or the ground state, and must proceed through the intermediacy of another excited state, suggested to be a triplet state. Analysis of the pressure dependence of CH 2CCl 2 yields gave the average energy transferred per gas kinetic collision as 17 ± 5 kcal mol −1 for self-deactivation and 16 ± 6 kcal mol −1 for deactivation by CF 4.

Laser isotope separation. Photochemical scavenging of chlorine-37 by bromobenzene

The photochemical reaction of iodine monochloride with bromobenzene yields chlorobenzene as enriched in either /sup 35/Cl or /sup 37/Cl depending on the excitation wavelength. A gas mixture of ICl and C/sub 6/H/sub 5/Br is irradiated by the output of a cw dye laser (01 A bandwidth) tuned to the (18,0) bandhead at 6053 A of the I/sup 37/Cl A /sup 3/II/sub 1/-X/sup 1/SIGMA/sup +/ system. At pressures of several Torr, C/sub 6/H/sub 5//sup 37/Cl is formed with a quantum yield of 10 percent and a maximum enrichment factor of 9 (75 percent /sup 37/Cl). The extent of enrichment is found to vary with starting conditions, permitting study of the mechanism for isotopically specific reaction and attendent scrambling pathways. Formation of C/sub 6/H/sub 5//sup 37/Cl involves direct reaction of I/sup 37/Cl* with C/sub 6/H/sub 5/Br to produce a vibrationally hot radical intermediate, which retains to a high degree its isotopic integrity because of more rapid elimination of Br atom than radical chain propagation. Comparison of iodobenzene with bromobenzene shows that the rate-limiting step must involve a Cl atom migration about the ring which is in competition with loss of Cl atom. While excited ICl transfers Cl to unsaturated halogenated hydrocarbons, nomore » reaction is observed with saturated halogenated hydrocarbons. The general form of this mechanism demonstrates isotopically specific synthesis involving reaction mixtures of natural abundance as starting materials.« less