Reactions Of Halogen Atoms Research Articles

Electronically Excited Complex Formation in Magnesium Cluster-Halogen Atom Reactions.

A near ultraviolet transition of Mg2F has been observed in emission from the reaction between magnesium clusters, most likely Mg3, and fluorine atoms. Because there is little evidence for upper-state internal excitation, the spectrum is assigned assuming that the upper state is quenched to its lowest vibrational levels. Two of possibly three ground-state vibrational frequencies, υ1 = 516 ± 10 cm-1 and υ2 = 104 ± 10 cm-1, have been established. Dispersed laser-induced fluorescence studies extrapolating on the observed chemiluminescence indicate an excited-state symmetric stretch frequency of order 370 ± 30 cm-1. Electronic structure calculations at the CCSD(T)/CBS level predict that the ground state of Mg2F has C2v symmetry and can be described as an Mg2+F- ion pair with two Mg-F bonds. Like the MgF A-X transition that is largely a transition between Mg orbitals, the observed transition in Mg2F is largely between orbitals on the magnesium dimer ion. The asymmetric C∞v Mg2+F- complex is also a minimum and is predicted to be 6.7 kcal/mol higher in energy. Calculated structures for the Mg2Cl isomers are also presented and used to further interpret the experimental results for the reaction of Mg clusters with Cl atoms. In contrast to Mg2F, the ground state of Mg2Cl is a linear C∞v MgMgCl structure with the C2v and D∞h isomers of the MgClMg structure slightly higher in energy.

Stretching the Polanyi Rules

Chemistry Forty years ago, Polanyi laid out a framework to explain and predict the relative effectiveness of translational and vibrational energy in driving the reactions of atoms with diatomics. The current frontier in state-resolved molecular dynamics research encompasses the reactions of halogen atoms with methane and its various isotopologues—a six-atom system. Over the past several years, successive experimental and theoretical studies have sought to clarify the extent to which the Polanyi Rules apply (or fail to apply) to such systems. For the reaction of chlorine with CHD3, the Rules suggest that the product-like transition state ought to favor the efficacy of vibration over translation, although the results of recent studies have been ambiguous in this regard. Zhang et al. now report quantum dynamics simulations of this reaction and compare their results with those from previous experiments and quasiclassical trajectories. The simulations suggest that C–H stretch excitation does indeed promote the reaction, except at collision energies below 1 kcal/mol. J. Phys. Chem. Lett. 10.1021/jz301649w (2012).

Dynamics of CN+alkane reactions by crossed-beam dc slice imaging

The hydrogen atom abstraction reactions of CN (X (2)Sigma(+)) with alkanes have been studied using the crossed molecular beam technique with dc slice ion imaging at collision energies of 7.5 and 10.8 kcalmol. The product alkyl radical images were obtained via single photon ionization at 157 nm for the reactions of CN (X (2)Sigma(+)) with n-butane, n-pentane, n-hexane, and cyclohexane. From analysis of the images, we obtained the center-of-mass frame product angular distributions and translational energy distributions directly. The results indicate that the products are largely backscattered and that most of the available energy ( approximately 80%-85%) goes to the internal energy of the products. The reaction dynamics is discussed in light of recent kinetics data, theoretical calculations, and results for related halogen and oxygen atom reactions.

A box model study on photochemical interactions between VOCs and reactive halogen species in the marine boundary layer

Abstract. A new chemical scheme is developed for the multiphase photochemical box model SEAMAC (size-SEgregated Aerosol model for Marine Air Chemistry) to investigate photochemical interactions between volatile organic compounds (VOCs) and reactive halogen species in the marine boundary layer (MBL). Based primarily on critically evaluated kinetic and photochemical rate parameters as well as a protocol for chemical mechanism development, the new scheme has achieved a near-explicit description of oxidative degradation of up to C3-hydrocarbons (CH4, C2H6, C3H8, C2H4, C3H6, and C2H2) initiated by reactions with OH radicals, Cl- and Br-atoms, and O3. Rate constants and product yields for reactions involving halogen species are taken from the literature where available, but the majority of them need to be estimated. In particular, addition reactions of halogen atoms with alkenes will result in forming halogenated organic intermediates, whose photochemical loss rates are carefully evaluated in the present work. Model calculations with the new chemical scheme reveal that the oceanic emissions of acetaldehyde (CH3CHO) and alkenes (especially C3H6) are important factors for regulating reactive halogen chemistry in the MBL by promoting the conversion of Br atoms into HBr or more stable brominated intermediates in the organic form. The latter include brominated hydroperoxides, bromoacetaldehyde, and bromoacetone, which sequester bromine from a reactive inorganic pool. The total mixing ratio of brominated organic species thus produced is likely to reach 10-20% or more of that of inorganic gaseous bromine species over wide regions over the ocean. The reaction between Br atoms and C2H2 is shown to be unimportant for determining the degree of bromine activation in the remote MBL. These results imply that reactive halogen chemistry can mediate a link between the oceanic emissions of VOCs and the behaviors of compounds that are sensitive to halogen chemistry such as dimethyl sulfide, NOx, and O3 in the MBL.

Heteronuclear and homonuclear surface abstraction reactions of Cl, Br, and F

Surface reactions of atomic halogen atoms play important roles in various plasma etching processes, commonly used in microlectronics manufacturing. However, relatively little is known about the surface chemistry of these key reactive intermediates. Previous measurements of the recombination coefficients of Cl, Br, and F on various surfaces in a molecular beam apparatus indicated that the recombination reaction is pseudofirst order [G. P. Kota, J. W. Coburn, and D. B. Graves, J. Vac. Sci. Technol. A 16, 270 (1998); 16, 2215 (1998)]. One mechanism that would result in pseudofirst order kinetics is a two-step process in which the first halogen atom adsorbs into a relatively strongly bound chemisorbed state, and the second atom reacts with it either through a direct reaction, or after being physisorbed onto the halogenated surface. In this article, we report experiments in which surfaces are first exposed to a molecular beam of one type of halogen atom, then the surface is exposed to a second type of halogen. During the second exposure, the heteronuclear reaction product is monitored with a mass spectrometer. Finally, the surface is sputtered and the mass spectrometer is used to detect any remaining presence of the original halogen atom. Analogous experiments were also performed with isotopically enriched mixtures of chlorine. These experiments unambiguously demonstrate that halogen atom surface recombination involves a two step adsorption-abstraction mechanism. Under all conditions studied, the surface recombination reactions proceeded at rates on the order of surface collision frequencies. The relative magnitudes of the heteronuclear rates (as a function of surface composition and halogen atom type) scaled in the same way as the homonuclear recombination probabilities measured previously. In every case examined, after the second halogen exposure, the surface retained a significant coverage of the halogen that had been originally exposed to the surface. This leads to the conclusion that only a fraction of the strongly bound surface sites are available for abstraction by free radical attack. Absolute calibration of the incident and evolved species fluxes allowed an estimate to be made of the reactive site densities for several surfaces. These ranged from 1012 to 1015 cm−2 depending on the surface.

Raman-like pumping from long range excited alkali atom-alkali dimer interactions

In a study of the reactions of halogen atoms with small supersonically cooled molecules, we observe the manifestation of Raman scattering in the absence of an external light source. The observed features are unique in that they are induced by and correlate with emission from the Na D-line components (D 1, D 2) formed in the chemical reaction, Na 2 + Br → Na ∗ + NaBr . In the chemiluminescent studies, the D-line emission is scattered by cooled sodium dimers (Na 2) formed, through supersonic expansion, in the lowest vibrational levels of their ground electronic state. Multiple Stokes and anti-Stokes features, assigned as resonance Raman progressions, dominate all normal chemiluminescent emission from the Na 2 B 1 Π u → X 1 Σ g + and A 1 Σ u + → X 1 Σ g + band systems. Comparison of higher resolution scans ( Δ ν ∼ 1.15 cm −1 ) with the results of computer simulations confirms the observation of resonance Raman scattering and suggests an unusually large broadening linewidth for the dimer, Γ ∼ 4 cm −1. This linewidth cannot be associated with Doppler or power broadening. Nor can it be attributed to interaction with the atomic bromine in the reaction zone. Pulsed and cw laser probes indicate that these bands are intimately linked to the presence of an excited state sodium atom (3P) constituency, suggesting the possibility of a long range Na 2Na ∗ interaction which mediates the Raman scattering process.

ChemInform Abstract: HOBr Kinetics: Reactions of Halogen Atoms, Oxygen Atoms, Nitrogen Atoms, and Nitric Oxide with HOBr.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Hypobromous acid kinetics: reactions of halogen atoms, oxygen atoms, nitrogen atoms, and nitric oxide with HOBr

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTHypobromous acid kinetics: reactions of halogen atoms, oxygen atoms, nitrogen atoms, and nitric oxide with HOBrP. S. Monks, F. L. Nesbitt, M. Scanlon, and L. J. StiefCite this: J. Phys. Chem. 1993, 97, 45, 11699–11705Publication Date (Print):November 1, 1993Publication History Published online1 May 2002Published inissue 1 November 1993https://doi.org/10.1021/j100147a025RIGHTS & PERMISSIONSArticle Views145Altmetric-Citations23LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (755 KB) Get e-Alerts

Reactions of recoil halogen atoms in liquid aqueous solutions of 5-bromouridine. Interaction and association of solutes and population distribution of associated species

Reactions of recoil halogen atoms in liquid aqueous solutions of 5-bromouridine. Interaction and association of solutes and population distribution of associated species

Extensions of the Melander–Westheimer Postulate: Isotope Effects in Reactions with Equilibrium Values Far from Unity

AbstractThe symmetric dependence of experimental primary kinetic isotope effects on the free energy change, obtained for reaction series with zero equilibrium isotope effects, can be inverted to obtain the free energy profile along the reaction coordinate. Trends in the kinetic isotope effects for the general case of non‐vanishing equilibrium effects can be understood by an extension of the same theory. Comparison is made with experiments for reactions of halogen atoms with hydrogen/deuterium molecules.

Luminescence of I2/Ar mixture flowing out of a quenching setup at atmospheric pressure

One of the possibilities for creating a population inversion on electronic transitions of molecules involves the use of radiative recombination reactions of halogen atoms. The prospects for this method have been justified theoretically, but there exist no experimental data. The present work was performed in order to obtain recombination radiation of molecular iodine in a high-temperature flow at atmospheric pressure. A single chamber plasmotron was used with a quenching setup and complete spectral and diagnostic apparatus. Pure argon exhibited a transparent flow, with a green luminescence arising upon the introduction of iodine. In the authors' opinion, the spectrum belongs to the system B..-->..X of the I/sub 2/ molecule and has a recombination origin. Three-particle photorecombination apparently predominates with the participation of the argon atom as a third body for stabilizing the quasimolecule. Amplification of the intensity of this radiation in a high-pressure flow requires refining the quenching setup and a more detailed study of the kinetics of the physicochemical and optical processes.

Erratum: Infrared chemiluminescence investigation of the reactions of halogen atoms with deuterated ethylene and benzene derivatives [J. Chem. Phys. 7 3, 1256 (1980)

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Statistical models for product energy distributions in bimolecular reactions with metastable intermediates

Detailed statistical model (phase space and adiabatic channel) calculations of product translational energy distributions P( E t) are presented for a typical example of the substitution reactions of halogen atoms with unsaturated hydro- (halo-) carbons. The influence of the reaction geometry and of potential parameters for the angular and radial potential is investigated as well as the possibility of incomplete vibrational excitation during the short (calculated) lifetime of the intermediate. A simple statistcal formula with one free parameter is proposed to be useful for fitting experimental data. Comparison with published P( E t) from molecular beam experiments suggests for the class of reactions in general and in particular also for the recent example Cl + C 2H 3Br → C 2H 3Cl + Br that there is no conclusive evidence against complete (“statistical”) vibrational excitation in the intermediate on time scales between 0.1 and 1 ps. Although no proof is possible that vibrational excitation actually is complete on that time scale, the major trends of the experimental P( E t) with molecular size, for example, can be predicted on the basis of that assumption and good fits of experimental P( E t) are possible with both detailed statistical calculations including the effects of the radial and the angular potential and with the simple statistical formula.

Infrared chemiluminescence investigation of the reactions of halogen atoms with deuterated ethylene and benzene derivatives

The technique of arrested relaxation infrared chemiluminescence has been used to investigate the reactions of halogen atoms with various deuterated olefinic and aromatic compounds. From infrared emission spectra of the products, the vibrational energy distributions were measured and then compared to the distributions resulting from statistical partitioning of energy. The reactions studied here are reactions of fluorine atoms with ethylene-d4, vinyl chloride-d3, vinyl bromide-d3, benzene-d6, toulene-d8, chlorobenzene-d5, and bromobenzene-d5 and the reaction of chlorine atoms with vinyl bromide-d3. Nonstatistical product energy distributions were observed for the F+ethylene-d4 and Cl+vinyl bromide-d3 reactions. All other reactions showed a statistical distribution of energy among the modes that were observed. The mechanism of distribution of energy among vibrational modes in intermediate size molecules is discussed in relation to these results.

Infrared chemiluminescent reactions of halogen atoms with hydrogen sulfide and methanethiol

Infrared chemiluminescence from HF and HCl has been observed to yield vibrational and rotational population distributions from the reactions F + H 2,H 2S, CH 3SH and Cl + H 2S, CH 3SH. An apparatus giving nearly arrested relaxation distributions is described. The cold wall reaction vessel is optically coupled with a commercial Fourier transform spectrometer. The following relative populations were determined: N υ=1: N υ=2: N υ=3 = 0.22:0.52:0.26 for F + H 2; N υ=1: N υ=2: N gn=3: N υ=4 = 0.26:0.33:0.27:0.14 for F + H 2S; N υ=1: N υ=2: N υ=3: N υ=4 = 0.31:0.35:0.30:0.04 for F + CH 3SH; N υ=1: N υ2 = 0.90:0.10 for Cl + CH 3SH. In the series F + H 2, H 2S, and CH 3SH the energy released as HF vibrational excitation ƒ υ = 0.64, 0.56 and 0.45, respectively) decreases with a reduction of the bond energy D 0 0(R-H) in the hydride. The bond energies D 0 0 (H-SH) ⩽ 388 kJ/mol and D 0 0 (CH 3S-H) ⩽ 366 kJ/mol follow from the HCl emission of the reactions Cl + H 2S - HCl(υ ⩽ 1) + SH and Cl + CH 3SH - HCl(υ ⩽ 2) + CH 3S(CH 2SH). The first value is consistent with the results of the F + H 2S studies. For F + CH 3SH, however, the energy corresponding to the highest observed HF (υ, J) levels is 12 kJ/mol less than the thermochemical limit set by the Cl + CH 3SH reaction. Evidence for both a CH 3S and a CH 2SH formation pathway exists.

The effect of the bond strength on the reactivity integral of displacement reactions of hot halogen atoms: The reaction of hot chlorine atoms with methyl iodide

The reaction of hot chlorine atoms with methyl iodide was studied as a function of the concentration of inert gas moderator and analyzed by the Estrup-Wolfgang kinetic theory. From the comparison of the reactivity integral for iodine displacement (0·29α ClAr) with those of chlorine and bromine atoms in methyl chloride and methyl bromide, respectively, the effect of the bond strength of CH 3- X is clearly proven.

Gas chromatographic separation of some labelled aromatic halogen compounds

Gas—liquid-chromatographic techniques for the separation of a large variety of mono-, di-and polysubstituted benzene derivatives from their multicomponent systems have been developed for the study of reactions of recoil halogen atoms with aromatic compounds. The18F,34mCl,38Cl,82Br and128I labelled benzene derivatives were produced by neutron irradiations of the corresponding liquid mixtures. Because of the short half-life of most of the isotopes in question a relatively fast method was required, therefore each of the techniques described takes less than one hour to achieve the separation.

Deuterium isotope effect in halogen atom reactions with methane and perdeuteriomethane at energies above thermal thresholds

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDeuterium isotope effect in halogen atom reactions with methane and perdeuteriomethane at energies above thermal thresholdsLeonard D. SpicerCite this: J. Am. Chem. Soc. 1973, 95, 1, 51–53Publication Date (Print):January 1, 1973Publication History Published online1 May 2002Published inissue 1 January 1973https://doi.org/10.1021/ja00782a009RIGHTS & PERMISSIONSArticle Views39Altmetric-Citations3LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (407 KB) Get e-Alerts Get e-Alerts

Atomic resonance fluorescence spectrometry for the rate constants of rapid bimolecular reactions. Part 2.—Reactions Cl + BrCl, Cl + Br2, Cl + ICl, Br + IBr, Br + ICl

Atomic resonance fluorescence spectrometry has been used to measure directly the rates of rapid bimolecular reactions of halogen atoms (2P) with halogen molecules at 298 K. Low concentrations of atoms (∼1011 atom cm–3) were generated in a flow system with a discharge-bypass. The following rate constants (cm3 molecule–1 s–1) are reported: Cl + BrCl → Cl2+ Br, k1=(1.45 ± 0.20)× 10–11; Cl + Br2→ BrCl + Br, k2=(1.20 ± 0.15)× 10–10; Cl + ICl → Cl2+ I, k3=(8.0 ± 1.0)× 10–12; Br + ICl → BrCl + I, k4=(3.0 ± 0.8)× 10–14; Br + IBr → Br2+ I, k5=(3.5 ± 0.6)× 10–11. k2 is equal to ∼0.5 of the hard sphere bimolecular collision frequency at 298 K.The values for k2 and k4 ae in good agreement with integral reaction cross sections determined in crossed molecular beams.

Reactions of Atoms

AbstractSeveral methods for the quantitative investigation of reactions of free atoms in the gas phase have been developed in recent years. The present article deals with reactions of hydrogen, carbon, oxygen, and halogen atoms with simple molecules. The results of such investigations are of fundamental importance for the understanding of chemical reactions and for many technical applications, such as explosion and combustion processes, halogenations, and chemical lasers.