Formation of SF5 in electron attachment to SF6; swarm and beam results reconciled

Based on the results of recent swarm experiments, it has been proposed that the increase in the cross section for SF₅⁻ formation observed at an electron energy, E_e of about 0.3 eV in electron beam studies of electron attachment to SF₆ is due to the combined (opposing) effects of the vibrational heating of the molecule by the attached electron, which enhances the dissociation of the nascent (SF₆⁻)^* ion, and the reduction of the cross section for capture (s-wave) of the electron by SF₆ with increasing E_e. Further, it has been shown that the dissociation reaction is endothermic by 0.12 eV, and that, contrary to previous suggestions, there is no potential barrier to this dissociation reaction. Now we have carried out electron beam studies of the SF₆ attachment reaction in Berlin at gas temperatures, T_g, over the range 300 to 920 K and in Innsbruck at T_g below 300 K. These studies have provided support for the above proposals concerning the appearance of the SF₅⁻ peak and for a reaction endothermicity of 0.12 eV. Thus these studies have clarified the doubts about the products of the SF₆ attachment reaction at low electron energy.     

Generation of Pulsed High-Energy Beams of Trifluoroiodomethane Molecules and Trifluoromethyl Radicals

A method for generating energetic beams of CF₃I molecules and CF₃ radicals was described. The method is based on the formation of pressure shock in front of a solid surface due to the impact of an intense, pulsed, gas-dynamically cooled molecular beam (or flow) on this surface and its use as a source of a secondary beam for producing energetic molecules. The secondary beam was formed upon efflux of molecules from the pressure shock through an orifice into a high-vacuum chamber compartment. The accelerated CF₃I molecular beam was generated by exciting the molecules with a powerful IR laser pulse in the pressure shock (in the secondary-beam source itself) and the beam of energetic CF₃ radicals was produced through the dissociation of CF₃I in either the pressure shock or the accelerated beam. High-density (10²⁰ molecule/(sr s)) beams of CF₃I molecules and CF₃ radicals with a kinetic energy of 1.2 and 0.4 eV, respectively, were obtained.     

三氟甲基磺酰氟绝缘介质理化特性的分子动力学模拟

采用分子动力学模拟方法, 研究了新型绝缘介质三氟甲基磺酰氟(CF₃SO₂F)的理化特性, 为高压电气设备应用CF₃SO₂F替代SF₆气体提供了理论依据. 基于量子化学计算的分子结构、 内转动、 偶极矩和振动频率等优化设计了mPCFF力场模型, 计算了243~323 K温度范围内CF₃SO₂F的各种气-液相平衡性质(饱和蒸汽压、 密度、 热容、 蒸发焓和临界参数等)与关键输运特性(扩散系数、 介电常数、 黏度和热导率等)基础参数, 并考察了CF₃SO₂F与N₂或CO₂形成混合气体的理化特性. 通过对比SF₆以及C4/CO₂混合环保绝缘气体, 针对混合比、 液化温度、 扩散和热导等因素提出了CF₃SO₂F的电气设备应用建议.     

Experimental and theoretical investigation of the reaction CF3 + NO + M → CF3NO + M from 0.5 to 12 Torr and from 253 to 373 K

The kinetics of the association reaction of CF₃ with NO was studied as a function of temperature near the low-pressure limit, using pulsed laser photolysis and time-resolved mass spectrometry. CF₃ radicals were generated by photolysis of CF₃I at 248 nm and the kinetics was determined by monitoring the time-resolved formation of CF₃NO. The bimolecular rate constants were measured from 0.5 to 12 Torr, using nitrogen as the buffer gas. The results are in very good agreement with recent data published by Vakhtin and Petrov, obtained at room temperature in a higher pressure range and, therefore, the two studies are quite complementary. A RRKM model was developed for fitting all the data, including those of Vakhtin and Petrov and for extrapolating the experimental results to the low- and high-pressure limits. The rate expressions obtained are the following: k₁(0) = (3.2 ± 0.8) × 10⁻²⁹ (T/298)^{−(3.4±0.6)} cm⁶ molecule⁻² s⁻¹ for nitrogen used as the bath gas and k₁(∞) = (2.0 ± 0.4) × 10⁻¹¹ (T/298)^(0±1) cm³ molecule⁻¹ s⁻¹. RRKM calculations also help to understand the differences in reactivity between CF₃ and other radicals, for the same association reaction with NO.     

Intermolecular potentials obtained from high-energy alkali scattering

Intermolecular potentials have been obtained from high-energy total cross sections for several alkali metal systems: CS + He, Ne, Ar, CH₃NO₂; K + CH₄, C(CH₃)₄, C₆H₆, c-C₆H₁₂, CH₃I, CCl₄, SF₆, N₂. For the CS-rare gas cases and K + N₂ only the repulsive part was determined. For the rest both attractive and repulsive parts were seen.     

Infrared diode laser spectroscopic detection of CF2 carbene produced by CO2 laser photolysis of CHCLF2

Infrared diode laser spectroscopy was applied to the detection of CF₂ carbene produced by CO₂-laser-induced dissociation of CHClF₂. Time-resolved spectra of CF₂ in several rotation-vibration states were observed. The initial concentration of CF₂ was estimated to be 5 × 10¹⁶ molecules cm⁻¹ from an analysis of the time-resolved spectra. The effect of Ar diluent on the time variation of the concentration of CF₂ is discussed.     

Intermolecular vibrational energy transfer of highly excited CF3I molecules observed from transient UV absorption spectra

Intermolecular vibrational energy transfer of highly excited CF₃I molecules by probing of the UV absorption band has been studied. The value of the rate constant of V---V exchange between ensembles of “hot” and “cold” molecules has been found to be 2 ± 0.4 μs⁻¹ Torr⁻¹. Consideration has been given to the effect of this process on isotopic selectivity loss in isotope separation by the method of successive IR-UV molecular photodissociation.     

PRODUCTION OF VINYL CHLORIDE IN THE INFRARED LASER INDUCED PHOTOSENSITIZED CHAIN REACTION OF 1, 2-DICHLOROETHANE

The chain reaction of 1, 2-dichloroethane was initiated by photosensitization of SF₆ under the selective excitation using a cw CO₂ laser.Vinyl chloride with high purity was produced in the reaction process.The initiation of the photosensitized chain reaction depends on the irradiated laser frequency.The mechanism of intermolecularr esonant transfer of vibrational energy has been discussed.     

Formation Mechanism and Emission Spectrum of AlO Radicals in Reaction of Laser－ablated Al Atom and Oxygen

IntroductionLaser ablation has been applied broadly toplasma production,cluster formation,nanometermaterial and thin film material preparation[1,2 ] .Us-ing spectroscopic technique and mass spectrometryto identify the transient species formed in the pro-cess could provide much useful information aboutthe prosperity ofplasma,the mechanism of materi-al growth[3 ,4] .Aluminum is an important metal material andwidely used in industry and daily life. To study thereaction mechanism of Al atoms with…     

Observation Of Mode Selective Vibrational Excitation Of SF6 By Collisions With 4–10 eV Li And H Ions

Structured time of flight spectra of both Li⁺ and H⁺ ions scattered from ground state SF₆, have been measured at angles (5.0° v_c.m. 16.6°) less than the rainbow angle at E_c.m., = 4.3 eV and 9.7 eV, respectively. The structure can be arttributed to vibrational excitation of the v₃ mode by H⁺ and excitation of the v₄ mode by Li⁺. The relative transition probabilities obey a Poisson distribution and can be explained by a simple forced oscillator model.     

Polymer chemistry. Part 1. Model compounds related to hexafluoropropenevinylidene fluoride elastomer

Model compounds related to the important elastomer derived from CH₂2=CF₂/CFCF₃ are synthesised from telomers (CF₃)₂CF(CH₂CF_2nI, by coupling and by fluorodeiodination reactions. These models, in reactions with bases, give information relating to mechanism of cross-linking of the polymer and indications of factors that limit its working life. Novel use of SbF₅ for dehydrofluorination in synthesis of fluorinated mono-enes and di-enes is described.     

Cluster-assistant generation of multiply charged atomic ions in nanosecond laser ionization of seeded methyl iodide beam

The photoionization of methyl iodide beam seeded in argon and helium is studied by time-of-flight mass spectrometry using a 25 ns, 532 nm Nd-YAG laser with intensities in the range of 2 × 10¹⁰–2 × 10¹¹ W/cm². Multiply charged ions of I^q+ (q = 2–3) and C²⁺ with tens of eV kinetic energies have been observed when laser interacts with the middle part of the pulsed molecular beam, whose peak profiles are independent on the laser polarization directions. Strong evidences show that these ions are coming from the Coulomb explosion of multiply charged CH₃I clusters, and laser induced inverse bremsstrahlung absorption of caged electrons plays a key role in the formation of multiply charged ions.     

Vibrational frequencies and structural determination of 1,1-difluoro-1,2-propadiene

The normal mode frequencies and corresponding vibrational assignments of 1,1-difluoro-1,2-propadiene in C_2v symmetry are examined theoretically using the 98 set of quantum chemistry codes. All normal modes were successfully assigned to one of 11 types of motion (C=C stretch, C–H stretch, C–F stretch, CH₂ scissors, CF₂ scissors, CH₂ wag, CF₂ wag, CH₂ rock, CF₂ rock, CF₂ twist, and C=C=C bend) predicted by a group theoretical analysis. Comparing the vibrational frequencies with IR and Raman spectra available in the literature, a set of scaling factors is derived. Predicted infrared intensities and Raman activities are reported. Predicted normal mode frequencies of 1,1-difluoro-1,2-propadiene-d₂ are reported.     

Photochemistry of perfluoroacyl halides in the presence of O2 and CO

Photolyses of CF₃C(O)X and C₂F₅C(O)X (X=Cl, F) at 254 nm in the presence of O₂ yield the perfluorinated radicals C₂F₅O (C₂) and CF₃O (C₁), respectively. The C₂ radicals decompose to give CF₃ radicals:

C₂F₅O→CF₃+CF₂O

which, in turn, react with O₂ leading to the formation of C₁ radicals. When in addition to O₂, CO is present, the C₁ radicals react with it leading to its catalytic oxidation to CO₂. The trioxide CF₃OC(O)O₃C(O)OCF₃ was observed following the photolysis of all four halides in the presence of O₂ and CO.

The other radical partners coming from the initial step in the photolysis (XC(O)) as well as the products of their reaction with O₂ (XC(O)O_y, y=1, 2) do not react with CO but when X=F they lead to the formation of a new stable peroxy molecule with the formula CF₃OC(O)O₂C(O)F. Some of the properties of this new molecule, its stability and its IR features are presented in this work.     

Spectroscopic behaviour, bond properties and charge distribution in methoxy groups in hydrofluoroethers: the effect of neighbouring CF2 group

A theoretical investigation is presented aimed to the interpretation of the spectroscopic behaviour of the methoxy group in molecules belonging to the class of hydrofluoroethers. The simulation of infrared and Raman spectra of four different stable conformers of CH₃–O–CF₂–CF₂–O–CH₃ and the comparison with the experimental spectra allow to propose a vibrational band assignment in the CH stretching region. This clarifies the role of the CF₂ group in determining the electronic properties and spectroscopic parameters of methyl CH bonds when back-donation of electronic charge take place from oxygen.     

Vibrational spectra and normal coordinate analysis of CF3 compounds Part XLVII. Vibrational spectra, normal coordinate analysis and electron diffraction investigation of CF3SiH3 and its deuterated varieties

The molecular structure of CF₃SiH₃ in the gas phase has been determined by electron diffraction analysis. Combined with a B₀ value derived from high resolution infrared spectra, this yielded r(SiC), 1.923(3) Å, r(SiH) 1.482(5) Å, r(CF) 1.348(1) Å, FCF 106.7(5)° and HSiH 110.3(10)° (r° values). The gas phase infrared and liquid phase Raman spectra of CF₃SiH₃, CF₃SiH₂D, CF₃SiD₃ have been measured and assigned, and force constants have been calculated by means of a normal coordinate analysis based on 52 experimental frequencies. The weakness of the SiC bond is confirmed by the low f(SiC) value of 2.54 N cm⁻¹. Infrared spectra recorded with a resolution of 0.04 cm⁻¹ at 240 K revealed rotational structure of vibrational bands. Rotational analyses of most parallel and a few perpendicular bands of CF₃SiH₃ and CF₃SiD₃ have been performed. Ground and excited state vibrational parameters have been obtained and used as supplementary data for the determination of the harmonic force field. Strong blending of all bands due to hot band cascades was noted.     

Use of central-field potentials for describing H2(D2) elastic scattering by other molecules

Differential elastic scattering cross sections have been measured for the systems H₂ + O₂, SF₆, NH₃, CO and CH₄ and for D₂ + O₂, SF₆, and NH₃ using crossed molecular beams. These experiments represent a wide variation in the size, anisotropy and initial relative collision energy E of the scattering partners, and of the corresponding de Broglie wavelengths. In all cases, rapid quantum oscillations have been resolved. From these differential cross sections, central-field potentials have been obtained which were independent of the energy and the isotopic composition of the hydrogen molecule used, as required for such potentials to be physically meaningful. Therefore, anisotropy effects do not seem important in describing the differential elastic scattering of these H₂(D₂) systems.     

Potential constants and Coriolis coupling constants of perhalogenated ethylenes Part 1. 1,1-Cl2C=CF2, 1,1-Cl2C=CBr2 and 1,1-F2C=CBr2

Coriolis coupling constants have been calculated from force field computations and used to evaluate the inertial defect of 1,1-dichlorodifluoroethylene, 1,1-dichlorodibromoethylene and 1,1-difluorodibromoethylene. The inertial defect values for the ground vibrational state of 1,1-C1₂C=CF₂ = 0.2450, 1,1-Cl₂C=CBr₂ = 0.3740 and 1,1-F₂C=CBr₂ = 0.4190 amu Ų show corrrespondence with the observed values of similar ethylene-type molecules.     

Gas-phase stability of cluster ions SF m + (SF6) n with m = 0–5 and n = 1–3

The gas-phase stabilities of cluster ions SF⁺_m (SF₆)_n with m = 0−5 were determined by using a high pressure mass spectrometer. The bond energies of SF⁺_m (SF₆)₁ were found to be less than 10 kcal/mol and to decrease with m = 0 → 5. There appear to be rather large gaps in the bond energies between n = 1 and 2 for the clusters SF⁺_m (SF₆)_n with m = 0−4. The structures of SF⁺₅, SF⁺ (SF₆)₁, SF⁺₃ (SF₆)₁, and SF⁺₅ (SF₆)₁ were investigated by ab initio molecular orbital calculations. For SF⁺₅, the D_3h geometry is found to be most stable andC_4v is a transition state of the Berry pseudorotation. For the ion-molecule complexes, the “on-top hat” models were found to be the most stable structures.