Gas‐phase reactions of Cl atoms with hydrochloroethers: relative rate constants and their correlation with substituents' electronegativities

Rate constants for the reactions of Cl atoms with CH₃OCHCl₂ and CH₃OCH₂CH₂Cl were determined at (296 ± 2) K and atmospheric pressure using synthetic air as bath gas. Decay rates of these organic compounds were measured relative to the following reference compounds: CH₂ClCH₂Cl and n‐C₅H₁₂. Using rate constants of 1.33 × 10^?12 and 2.52 × 10^?10 cm³ molecule^?1 sec^?1 for the reaction of Cl atoms with CH₂ClCH₂Cl and n‐C₅H₁₂, respectively, the following rate coefficients were derived: k(Cl + CH₃OCHCl₂) = (1.05 ± 0.11) × 10^?12 and k(Cl + CH₃OCH₂CH₂Cl) = (1.14 ± 0.10) × 10^?10, in units of cm³ molecule^?1 s^?1. The rate constants obtained were compared with previous literature data and a correlation was found between the rate coefficients of some CH₃OCHR¹R² + Cl reactions and ΔElectronegativity of ? CHR¹R². Copyright © 2008 John Wiley & Sons, Ltd.     

The methyl bromide molecule: A critical consideration of perturbations in spectra

This work gives an extensive critique of studies on methyl bromide and all its isotopic varieties with special stress on their rotational, vibrational, and rovibrational spectra. The rotational constants of more than 40 vibrational states of CH₃Br and 20 of CD₃Br, as well as of the ground states of all varieties, were critically examined and corrected where needed. An almost complete set of harmonic and anharmonic constants for CH₃Br was derived. From the set of rotation-vibration interaction constants, new accurate equilibrium constants A_e and B_e have been evaluated for CH₃⁷⁹Br, CH₃⁸¹Br, CD₃⁷⁹Br, CD₃⁸¹Br, from which the following equilibrium structure is obtained: r_e(C---H) = 1.0823 Å; r_e(C---Br) = 1.9340 Å; α(HCH) = 111.157°.     

Line Intensities in the ν6 Fundamental Band of CH3Br at 10 μm

Fourier transform spectra have been obtained at 296 K at a resolution of 0.002 or 0.004 cm^-1 depending on the pressure range. Line positions and intensities of CH₃⁷⁹Br and CH₃⁸¹Br belonging to the fundamental band ν₆ were measured and analyzed between 890 and 1080 cm^-1. A total of 2896 (2838) line positions with J≤60 and K≤6 was fitted with a root-mean-square deviation of 0.00028 (0.00021) cm^-1 for CH₃⁷⁹Br and CH₃⁸¹Br, respectively, within the experimental accuracy. The fit to 316 (312) measured intensities yielded values of the dipole moment derivatives of both isotopes with a standard deviation of 5% to be compared to an experimental uncertainty equal to 6% or better. A prediction of the line positions and intensities has been generated for atmospheric purposes with all lines from 820 to 1120 cm^-1 with intensities greater than 10^-5 cm^-2 atm^-1.     

Submillimeter spectrum of methyl bromide (CH3Br)

Methyl bromide is a ubiquitous component of the atmosphere, but has yet to be remotely detected in the upper atmosphere. Due to the strong ozone depletion capability of the activated bromine species, the total atmospheric bromine load needs to be carefully monitored. Combined analysis of precise measurements and cataloging of the rotational spectrum of methyl bromide may enable its concentration to be monitored with future remote sensing instrumentation. In an effort to extend and improve previous work for this molecule, the spectrum of CH₃Br has been measured at JPL. Using an isotopically enriched ¹³CH₃Br (90%) sample, spectra have been recorded from 750 to 1200 GHz. Quantum number assignments cover the CH₃⁷⁹Br, CH₃⁸¹Br, ¹³CH₃⁷⁹Br and ¹³CH₃⁸¹Br isotopologues with J < 66 and K < 17 for the ground and ν₃ vibrational states. The dataset for the ¹²C isotopologues is more precise than previous THz measurements resulting in reductions of rotational and distortion parameter uncertainties by factors of 2-15. Parameters of the ν₃ state of the ¹²C isotopologues are improved by 2-105. The spectra of the ¹³C isotopologues are the first reported beyond J = 2.     

The Syntheses,Structures, Fluorescence Properties and Biological Activity of two Novel Zinc(II) Complexes Controlled by the Tripodal Imidazole Ligand

Two new zinc complexes, namely Zn(L¹)ClCH₂NO(1) and {Zn(L²)CH₂NO}_n?N(CH₃)₃?ClO₄(2) (L¹ = 3,5-di(1H-imidazol-1-yl)pyridine L² = 1,3,5-tris(1-imidazolyl) benzene), have been synthesized, and characterized by IR spectra, elemental analysis, and a single crystal X-ray diffraction. Fluorescence spectroscopy indicated that two complexes presented strong DNA binding affinity constants to fish sperm DNA (FS-DNA). Gel electrophoresis assay demonstrated the ability of the complex to cleave the HL-60 DNA. Apoptotic study showed the complex exhibited significant cancer cell(KB) inhibitory rate.     

Effect of electron scavengers on the gamma radiolysis of H2S-Ch3Br systems

Abstract

The mechanism of mixed dimer negative ion formation in the gamma radiolysis of the gaseous system hydrogen sulphide-methyl bromide has been investigated using carbon tetrachloride and chloroform as the electron scavengers. The concentration of methane was measured gas-chromatographically. The measurements were performed at different total pressures.

ΔG(CH4)-1 is a linear function of [CH³Br][H2S]2/[Sc] (where Sc═CCl4 or CHCl3). On the basis of the above dependencies the mechanism of the formation of the (CH³Br-H³S)? ion was confirmed and the rate constant was calculated to be k=K-ka-kc/ka = 6.5 ×l0^?49 cm⁹ molecule ^?3s^?1     

Reactions and anion desorption induced by low-energy electron exposure of condensed acetonitrile

Thermal desorption spectrometry (TDS) and electron stimulated desorption (ESD) are employed to investigate mechanisms responsible for the formation of C₂H₆ in electron irradiated multilayer films of acetonitrile (CH₃CN) at 30 K. Using a high sensitivity time-of-flight mass spectrometer, we observe the ESD of anionic fragments H⁻, CH₂ ⁻, CH₃ ⁻ and CN⁻. Desorption occurs following dissociative electron attachment (DEA) via several negative ion resonances in the 6 to 14 eV energy range and correlates well with a “resonant” structure seen in the TDS yield of C₂H₆ (i.e., at mass 30 amu). It is proposed that C₂H₆ is formed by the reactions of CH₃ radicals generated following DEA to CH₃CN which also yields CN⁻. Between 2 and 5 eV, a second resonant feature is seen in the C₂H₆ signal. While DEA is observed in the gas phase at these energies, no anion desorption occurs since anionic fragments likely have insufficient kinetic energy to desorb. Since the CH₂ ⁻ ion has not been observed in gas-phase measurements, we propose that it is formed, along with HCN (that is detected in TDS) when dissociation into CH₃ ⁻ and CN is hindered by adjacent molecules.     

Electronic excitation of HgX (X = Cl,Br, I) due to electron and methyl mercury halide collisions

Electronic excitation of HgX (X = Cl, Br, I) radicals in the B-state has been observed as the result of collisions with low energy electrons and methyl mercury halide (CH₃HgX) molecules. The emission intensity has been observed to be much weaker than that observed for electron-HgX₂ collisions under similar experimental conditions. Using the strongest band head of the B-X band system, an attempt has been made to calculate the emission cross section due to electron CH₃HgX collisions at 10 eV electron kinetic energy. For HgCl, HgBr, and HgI radicals, these cross sections are 1 × 10^-18, 7 × 10^-17, and 2 × 10^-17 cm², respectively, with an estimated uncertainty of ±30%. Our measured threshold electron energy for excitation of CH₃HgX molecules and observation of the B-X emission band system and emission cross sections measured at 10 eV are greatly different from those measured by Allision and Zare [Chem. Phys. 35, 263 (1978)].     

The microwave spectrum of silyl isocyanate, SiH3NCO: Spectra of isotopically substituted species and correction of the rs structure

Microwave spectra have been measured for 10 isotopic species of silyl isocyanate, SiH₃NCO, in the ground vibrational state, and in several excited states of the lowest frequency bending vibration, ν₁₀. This vibration is highly anharmonic, with a potential hump of 31.5 cm⁻¹ at the linear configuration, and its effects have been removed from the rotational constants to produce effective ground-state rotational constants B₀^* for each isotopic species. These B₀^* constants have been used to determine the structural parameters, which are now in good agreement with earlier electron diffraction values. Excellent predictions have been made of the centrifugal distortion constants for different isotopic species and vibrational states, as well as of the l-type doubling constants of the various isotopic species.     

The fragmentation of negative ions of fullerene C60 trifluoromethyl derivatives

The formation and decay of gas-phase negative ions of trifluoromethylated fullerenes C₆₀(CF₃) _n (n = 2–10) were studied. The resonance electron capture mass spectra were measured to find that the main fragmentation channel of negative ions was the detachment of trifluoromethyl groups. The degree of fragmentation directly depended on the energy of electrons and reached the complete splitting off of all the CF₃ addends with the formation of C₆₀⁻ ions. The observed metastable ion signals were analyzed to determine the scheme of sequential fragmentation of negative ions.     

Temperature dependence of self- and N2-broadening coefficients of CH3Br ν6 band

Using absorption FT spectra (Bruker IFS 120, unapodized FWHM resolution ≈0.001 cm⁻¹), about 1400 lines, between 880 and 1050 cm⁻¹, and belonging to the ν₆ band of both ¹²CH₃⁷⁹Br and ¹²CH₃⁸¹Br isotopologues have been studied. Self- and N₂-broadening coefficients are measured at various temperatures with an accuracy estimated to be around 10%. Their temperature-dependence exponents n_self and n_N2 have been derived with an accuracy estimated to be between 10% and 20%. A rotational dependence with the quantum number J has been observed for both n_self and n_N2, and has been empirically modeled using average values and polynomial expansions.     

New ground state constants of CH3Cl and CH3Cl from global polyad analysis

A global analysis of the infrared spectrum of chloromethane involving the ground state and the 13 vibrational states lying up to 2600 cm⁻¹ was recently achieved using high resolution Fourier transform spectra of pure isotopomers. More than 20 000 transitions (cold and hot bands) for each isotopomer ¹²CH₃³⁵Cl and ¹²CH₃³⁷Cl have been assigned and fitted with a standard deviation of about 3 × 10⁻⁴ cm⁻¹ close to the experimental precison. As part of this global effort, improved ground state constants up to sextic centrifugal distortion terms have been determined for each isotopomer taking advantage of the numerous allowed and perturtation-allowed transitions simultaneously fitted using our global model. The axial constants could be determined from ΔK ≠ 0 combinations arising from rovibrational local resonances within Polyads 3 and 5.     

Study of processes of translational,rotational, and vibrational relaxation based on CARS spectra line shapes

This paper reviews the various physico-chemical processes responsible for actual linewidths encountered in high-resolution coherent anti-Stokes Raman spectroscopy (CARS). Most of the experimental data are based on linewidth measurements using a pulseamplified CARS spectrometer with an emission bandwidth (FWHM) of 2×10^–3 cm^–1. Detailed rotational and vibrational relaxation constants have been obtained from the analysis of theQ-branch profiles of C₂H₂, N₂, CH₄, and SiH₄.     

Doppler-limited dye laser excitation spectroscopy of the HSO radical

The cw dye laser excitation spectrum of the vibronic transition of the HSO radical was observed between 16 420 and 16 520 cm⁻¹ with Doppler-limited resolution, 0.03 cm⁻¹. The HSO radical was produced by reaction of discharged oxygen with H₂S or CH₃SH. The observed spectra were assigned to 751 transitions of the K′_a ← K″_a = 2 ← 3, 1 ← 2, 0 ← 1, 1 ← 0, 2 ← 1, and 3 ← 2 subbands, and were analyzed to determine rotational constants, centrifugal distortion constants, and spin-rotation interaction constants with good precision. The signs of the spin-rotation interaction constants were determined for both the upper and the lower state from the observed spectra. The band origin obtained is 16 483.0252 (2.5σ = 0.0013) cm⁻¹. The molecular constants which were determined reproduce the observed transitions with an average deviation of 0.0045 cm⁻¹.     

New analysis of the Coriolis-interacting v2 and v5 bands of CH3Br and CH3Br

The and fundamental bands of CH₃⁷⁹Br and CH₃⁸¹Br have been studied by Fourier transform infrared spectroscopy with an unapodized resolution of 0.004 cm⁻¹, corresponding to an improvement of one order of magnitude compared to previous studies. For both isotopomers, some 2427 (2239) lines were newly assigned for the parallel and the perpendicular bands and, in addition, 80 perturbation-allowed transitions were also added. The ground-state axial rotational constants A₀ were redetermined from allowed and perturbation-allowed infrared transitions observed in the v₂ and v₅ bands around the local crossing. The A₀ values obtained for both isotopomers are more accurate but fully compatible with those obtained previously. Using those results, and the variation of the rotational constants with vibration, new accurate equilibrium constants A_e and B_e have been also determined for CH₃⁷⁹Br and CH₃⁸¹Br. The excited states v₂=1 and v₅=1 are coupled by Coriolis-type interactions (Δl=±1,ΔK=±1) and (Δl=?1,ΔK=±2), while the l₅=±1 levels of v₅ interact also through “l(2,2)”-type interaction (Δl=±2,ΔK=±2). The Coriolis coupling term was determined to be for CH₃⁷⁹Br and for CH₃⁸¹Br. All interaction parameters have been determined with higher accuracy, compared to previous studies. A total of 4213 (3704) line positions with J?68(64) and K?16(11) including all available data was fitted using 20 (18) parameters with a root-mean-square deviation of 0.0007 (0.0006) cm⁻¹ for CH₃⁷⁹Br and CH₃⁸¹Br, respectively. Two different but equivalent forms of reduced Hamiltonians with two different sets of constrained constants were successfully applied according to Lobodenko's reduction [J. Mol. Spectrosc. 126 (1987) 159]. The ratio of the transition moments, |d₂/d₅|=1.65, and a positive sign of the Coriolis intensity perturbation d₂×ζ₂₅×d₅ were determined. Therefore, it has been possible to generate an accurate prediction of the whole spectrum between 1200 and 1650 cm⁻¹, including Q branches.     

Negative ion photoelectron spectroscopy of 2,2’-bithiophene cluster anions, (2T)n - (n = 1–100)

Cluster anions of 2,2’-bithiophene, (2T)_n^-, were produced up to n ∼500 in the gas-phase. The energetics of the excess electron in the (2T)_n^- clusters with n =1-100 were explored by negative ion photoelectron spectroscopy. When the vertical detachment energies (VDEs) obtained from the photoelectron spectra were analyzed by a plot against n^-1/3, it has been revealed that the excess electron trapping level thus extrapolated is located at ∼0.8 eV below the conduction band minimum (i.e. LUMO) of the 2T thin film. The large slope of the VDEs vs. n^-1/3 plot suggests that the neutral 2T molecules surrounding the anion core take non-planar twisted conformations with permanent dipole moments, resulting in the exceedingly deep trapping of the excess electron in the 2T cluster anions.     

Pulsed ESR and molecular motions

The possibilities of applying three different pulsed ESR techniques have been considered: 1. Phase relaxation measurements by electron spin echo (ESE) affords the estimation of the correlation time of the motion in the region up to 10^?5 s. The results of theoretical and experimental analysis of the effect of methyl group rotation in nitroxide radicals have been proposed. 2. The method of pulsed saturation involving detection of ESE signal allows the range of the measured times to be extended up to the values of about 10^?2 s. The rotation of CH₂ group in the CH₂CO₂ ^? radical and that of the CH₃ group in the CH₃CHCO₂ ^? radical have been investigated. 3. The method of pulsed saturation combined with pulsed scanning of H₀ allows the analysis of the rotationally induced redistribution of the pulsed saturation throughout the ESR spectra of the radicals. This version of pulsed ESR has been used to study the mobility of nitroxide spin labels.     

N2 production in e-beam pumped XeF lasers containing NF3

The rate of build-up of N₂ was measured in electron-beam-irradiated Ne/Xe/NF₃ mixtures using mass spectroscopy. the amount of N₂ produced indicated that N₂ is the primary nitrogen bearing stable species created in these mixtures. The rate constant for dissociative electron attachment to the NF₂ fragments produced in electron attachment to NF₃ is estimated to be 5×10^–8 cm³/s in order to explain the amount of N₂ produced.This work was supported by DARPA under Contract No. DAA01-82-C-A125 and monitored by MICOM     

The microwave spectrum of 1-phosphabut-3-ene-1-yne, CH2=CHCP

The new molecule 1-phosphabut-3-ene-1-yne, CH₂=CHCP, produced by pyrolyzing prop-1-ene-3-phosphorus dichloride, CH₂=CHCH₂PCl₂, was detected by microwave spectroscopy. The analysis of the rotational transitions indicates that the molecule is planar with constants: A₀ = 46 694(24), B₀ = 2807.7100(21), and C₀ = 2645.8356(21) MHz. These rotational constants indicate that the structure of the vinyl group is essentially the same as that in CH₂=CHCN and CH₂=CHCCH; r(C---C) = 1.432 Å and (C=C---C) = 123.9°. The dipole moment parameters are μ_A = 1.181(2), μ_B = 0.074(1), and μ = 1.183(2) D. The vibrational satellite spectra for the C---CP bending modes indicate that ν₁₁(a′) = 184 ± 30 cm⁻¹ and ν₁₅(a″) = 263 ± 30 cm⁻¹.     

Experimental study of carbon particle charging at shock-wave pyrolysis of C3O2

The temporal variation in electron and ion concentrations have been measured in shock-heated mixtures of Ar + (0-2)% C₃O₂ in the 2000-3600 K temperature and 15-30 bar pressure range. Experiments in pure argon proved that the observed free electrons and ions originate from inherent impurities of sodium. The equilibrium concentrations of free charges in argon were established during (1-3) × 10⁻⁵ s and varied from 4 × 10¹¹ cm⁻³ at T₅ = 2500 K to 5 × 10¹² cm⁻³ at 3500 K. In the reactive mixtures, containing C₃O₂, the time profiles of electron and ion concentrations showed a more complicate behavior—a fast rise to a maximum followed by a gradual decay. The maximum ion concentrations were much higher and electron concentrations were much lower than in similar conditions in argon. The extent of the subsequent decay of electron concentration increased proportionally to the square of the C₃O₂ concentration. In the mixture with 2% C₃O₂ the final electron concentration was about 100 times less than in pure argon. The characteristic decay time of free charges varied from 400 to 40 μs and decreased proportionally to the square root of the charge concentration. The data analysis is based on the assumption that the observed redistribution of electron and ion concentrations is caused by charging of the carbon particles formed during pyrolysis of C₃O₂. The kinetics of particle charging and the final distribution of charges were evaluated by the analysis of electron and ion fluxes to the particles in accordance with the electric potentials of charged particles and corresponding sodium ionization. A predominance of negatively charged particles, caused by the high electron mobility, resulted in their much higher concentration than the concentration of free electrons.