Reactive scattering of a neon seeded oxygen atom beam

A high pressure microwave discharge source operating with a dilute mixture of O₂ in Ne has been used to produce a supersonic nozzle beam of O atoms seeded in Ne. This low energy supersonic O atom beam has been used to study the reactive scattering of O atoms with Cl₂ and CS₂ molecules at an initial translational energy E = 13 kJ mol^?1. The results are compared with rective scattering from the same reactions using a high energy O atom beam formed by seeding O atoms in He. The O + Cl₂ reaction proceeds via a short-lived collision complex where the lifetime of the collision complex depends upon the initial translational energy. However the O + CS₂ reaction follows a stripping mechanism which is unaffected by initial translational energy.     

Dynamics of reactions of O(3P) atoms with CS,CS2 and OCS

The reactions of CS(X ¹Σ⁺), CS₂(X ¹Σ⁺_g) and OCS(X ¹Σ⁺) with O(³P) were studied at 298 K by means of a CO laser resonance absorption technique. The CO(ν) population distribution produced from the reaction O(³P) + CS(X ¹Σ⁺) studied in a quartz flash photolysis tube (λ>/ 200 nm) is similar to distributions observed previously for ν> 7. For ν < 7 an energetically colder vibrational population was observed which is attributed to the reaction of O(³P) atoms with undissociated CS₂(X ¹Σ⁺_g). Subsequent experiments carried out in a Pyrex flash photolysis tube (λ>/ 300 nm) in which the O(³P) + CS₂(X ¹Σ⁺_g) reaction is the only one which can occur confirmed that the colder population observed is attributable to this process. The branching ratio for the reaction channel O(³P) + CS₂(X ¹Σ⁺_g) → CO(X ¹Σ⁺) + S₂(³Σ^?_g) has been measured. We find that 1.4 ± 0.2% of the O + CS₂ reaction proceeds through this channel, and that the rate constant for this reaction channel is, k = 3.5 (±0.5) × 10¹⁰ cm³/mole s. Isotope labeled experiments using ¹⁸O atoms show that the O(³P) + OCS(X ¹Σ⁺) reaction takes place by a direct stripping mechanism, wherein CO(ν) is produced exclusively from the parent OCS molecule. The CO(ν) formed in this reaction carries about 9% of the total available energy.     

Rate constant and products of the reaction Cl + CS2 in air

A steady-state system involving the photolysis of Cl₂ as a source of Cl has been used to investigate the reaction of Cl with CS₂ at 293 ± 3 K in a 420 l reaction chamber coupled to FTIR and mass spectrometers. Using a relative rate technique, the measured effective rate constant was found to be dependent on the total pressure and mole fraction of O₂ present in the system. In 760 Torr synthetic air, the overall rate constant for the Cl + CS₂ reaction is(0.83 ± 0.17) × 10⁻¹³ cm³ molecule⁻¹s⁻¹. SO₂, COS and COCl₂ are the main reaction products.     

Molecular beam study of iodine atom abstraction by oxygen atoms

Reactive scattering of O atoms with CF₃I molecules has been studied at an initial translational energy E = 32.1 kJ mol^?1 using a He seeded O atom beam and at E = 13.9 kJ mol^?1 using a Ne seeded O atom beam. Reactive scattering of IO product favours the backward hemisphere at low energy but becomes almost isotropic at high energy. The product translational energy distribution at low energy indicates substantial energy transfer with internal modes of the collision complex but at high energy the excess energy is disposed into product translation.     

Reactive scattering of hydrogen and deuterium atoms. III. Angular distributions for ClNO,SCl2, S2Cl2, SOCl2 and ClF3

Angular distributions for reactive scattering of hydrogen and deuterium atoms from five polyatomic molecules have been measured. With the exception of DCl from D + SCl₂ all angular distributions have a backward or sideways maximum.A measurement of the phase of the reactive signal shows that only 20% to 40% of the available energy goes into translation. Good agreement is found with a low pressure chemiluminescence experiment for H + SCl₂, while some differences are found for the higher pressure studies of H + S₂Cl₂ and H +SOCl₂. From the D + ClF₃ study some comments can be made on the reaction paths of the H₂ClF₃ chemical laser.     

Stimulated CO emission of the (1 → 0) band in a pulse initiated (CS2 + O2) chemical laser

Chemi-excitation of CO^(v) to generate stimulated emission by v = 1 → 0 transitions has been achieved in CS₂ + O₂ + He mixtures, initiated by 13 kV pulses. The discharge is impressed axially along the laser tube. Rotational lines ranging from P(14) to P(10) have been observed. This partial inversion occurs only under strictly controlled conditions.     

Improved study of the ionization of hydrogen atoms in thermal energy collisions with metastable He(23 S) atoms

The first electron spectrometric study of the ionizing reaction of metastable He(2³ S ₁) atoms with ground state hydrogen atoms has been carried out with sufficiently high resolution to partially resolve the rotational structure due to formation of rovibrationally excited HeH⁺ (v, J) ions at two different beam source temperatures (300 K and 90 K). The electron energy spectrum has been reproduced in model quantum calculations, using a new large scale ab initio calculation of the He(2³ S)+H(1² S)²Σ-potential. The imaginary part has been adjusted to yield a satisfactory fit to the measured spectrum. The collision energy dependence of the associative ionization electron spectra and of the total and partial ionization cross sections is discussed in some detail. No significant signs for limitations of the used local complex potential method, indicated by results of an earlier study of the He(2³ S)+H(1² S) system, have been found in the present work, in which the calculations were carried out with an improved and corrected program.     

OCS formation in the reaction of OH with CS2

A steady-state system involving photolysis of HONO as a source of OH was used to investigate the reaction of OH with CS₂ at 1 atm and 295 K. In the presence of O₂ ( > 40 Torr) a rapid reaction of OH with CS₂ occurs giving OCS. At lower O₂ concentrations, OCS formation ceases. In air the overall rate constant for OH + CS₂ → OCS was (1.7 ± 0.9) × 10^?12 cm³ molecule^?1 s^?1.     

On the use of mass scaled cluster coordinates to describe polyatomic molecule reaction dynamics: Application to O + CS2 → SO + CS

We explore the use of mass scaled cluster coordinates to describe polyatomic molecule reaction dynamics. These coordinates provide the natural extension to polyatomic systems of the familiar atom—diatom model of “rolling a marble” on a skewed and scaled potential surface in that they reduce the kinetic energy of an arbitrary system to one equivalent to that of a single mass point moving in 3N - 3 dimensions. For any given number of atoms, usually several distinct types of mass scaled cluster coordinates can be introduced, all of which are interrelated by orthogonal transformations, and many of which are convenient for describing trajectory motion in one or more arrangement channels. We illustrate these points by an application to the collinear O + CS₂ → SO + CS reaction. For this system, the reagent to product coordinate transformation is conveniently described in terms of two Euler angles α and β, for which β is analogous to the atom—diatom skew angle, and α determines how the reagent vibrational normal modes relate to the product degrees of freedom. Examination of trajectory behavior indicates that the rather small value of π - α (21.7°) leads to a rather clean correlation between CS₂ asymmetric stretch motion and product CS vibrational motion, and between CS₂ symmetric stretch and a combination of SO stretch and product translation. This explains why symmetric stretch mode excitation enhances the O + CS₂ reaction rate more efficiently than asymmetric stretch mode excitation. We also find for O + CS₂ (and many other reactions for which the unbroken bond does not significantly change its length during the reaction) that the reagent and product segments of the minimum energy path are coplanar. This means that a natural partitioning of the reaction dynamics exists in which motions parallel to this plane tend to be active in promoting the reaction whereas motions perpendicular tend to be inactive. A study of trajectory motions and product state energy partitioning for O + CS₂ confirms this.     

Redox and oxo-abstraction Reactions of Silylamine with MoOCl4

Trimethylsilyldiethylamine Me₃SiNEt₂ and MoOCl₄ (1:1) undergo a free radical redox reaction in CH₂Cl₂ or Et₂O to form MoCl₃O(HNEt₂). Reduction occurs even in aprotic media like CCl₄ and CS₂ to give Mo^V complexes Mo₂Cl₆O₂(N₂Et₄) and Mo₂Cl₆O₂[(SCNEt₂)₂S₂], respectively. A 2:1 reaction in nonionizing protic solvents undergoes redox cum cleavage to provide MoCl₂O(NEt₂) (HNEt₂) but a reaction at reflux temperature in 1,2-dichloroethane leads to diethylammonium salt, [Et₂NH₂][MoCl₄O(HNEt₂)]. Higher molar reactions (3:1, 4:1) in CH₂Cl₂ or Et₂O are associated with redox reaction as well as oxygen atom abstraction to form de-oxo Mo^IV complex MoCl₃(NEt₂)(HNEt₂)₂, whereas, a 3:1 reaction in CS₂ forms Mo₂Cl₄O(S₂CNEt₂)₄. Compounds have been characterized by elemental analyses, redox titration, magnetic moment, conductance, infrared, electronic absorption and ¹H-NMR measurements.     

Gas phase reactions of Cl2O with X−(D2O)n=0–4 (X = O,OD, O2, DO2, and O3)

The reactions of Cl₂O with the cluster ions X⁻(D₂O)_n=0–4 (X = O, OD, O₂, DO₂, and O₃) were studied in a He buffer gas at temperatures within the range 171–298 K and pressures of 0.27–0.51 Torr, using a flow-tube apparatus. All ions were found to react with Cl₂O at rates slower than predicted by the collision rate and the charge center was transferred from X⁻ to Cl⁻ or ClO⁻. The primary product ions Cl⁻(DOCl) and ClO⁻(DOCl) were observed to react further to produce the ions Cl₃O⁻ and Cl₃O₂⁻. The rate constants for the observed reactions are reported and the role that thermodynamics plays in determining possible reaction channels is discussed.     

Fluorescence and recombination-emission spectra from S2 formed by ultraviolet laser photolysis of CS2 in an argon matrix at 15 k

Two series of emission bands were observed for the CS₂/Ar(1 : 100–500) system at 15 K with excitation at 257.3 nm. They are assigned to B³Σ^?_u → χ³Σ^?_g and B″³Π_u → X³Σ^?_g of S₂, which was formed by photodissociation of CS₂, CS₂ + hv → CS + S, followed by recombination of two S atoms. The B″³Π_u state has been found 524 cm^-1 lower in energy than B³Σ^?_u     

A study of the reaction O + CS2 → SO + CS using crossed molecular beams

Measurements of SO scattering from the reaction O + CS₂ → SO + CS using crossed thermal molecular beams show that (a) there is strong forward sca     

Strength of the PtCS2 bond in Pt(PPh3)2(CS2)

The enthalpy of the reaction: Pt(PPh₃)₂(CH₂CH₂)(cryst.) + CS₂(g) → Pt(PPh₃)₂(CS₂)(cryst.) + CH₂CH₂(g) has been determined as ΔH = ? 4.40 ± 2.2 kJ mol^?1 from solution calorimetry, and the bond dissociation energy D(PtCS₂) shown to be slightly greater than D(PtC₂H₄).     

The coordination and activation of carbon disulfide in binuclear rhodium complexes

The reaction of trans-[RhCl(CO)(DPM)]₂ (DPM = Ph₂PCH₂PPh₂) with CS₂ yields an interesting series of CS₂ complexes culminating in the condensation of two CS₂ molecules yielding the unusual, asymmetric species [Rh₂Cl₂(CO)- (C₂S₄)(DPM)₂]. This novel C₂S₄ species is also produced in the reaction of [Rh₂Cl₂(μ-CO)(DPM)₂] with CS₂. The structural determination of the C₂S₄ complex indicates that the C₂S₄ moiety bridges the rhodium atoms such that it forms a R$\text{hSCSC}$ metallocycle with one rhodium atom while simultaneously bonding through a sulfur atom to the second rhodium atom forming a R$\text{hCSR}$h metallocycle. A scheme for the reactions of the above complexes with CS₂ is presented.     

Monte Carlo simulation of RRKM unimolecular decomposition in molecular beam experiments. V. product ox angular and energy distributions from O(3P)+X2 (X = Br,I)

Statistical simulation was applied to the unimolecular decomposition of the collision complexes formed in the crossed beam experiments on O(³P) + Br₂ by Fernie et al. and O(³P) + I₂ by Durkin et al. The simulation procedure used the fundamentals of RRKM theory and included exact angular momentum conservation. The impact parameter distributions were varied to obtain the best fits. Good agreement with experimental laboratory angular distributions measured with O atoms seeded in both He and Ne was found for impact parameter distributions which were peaked at quite small values, in most cases between 2 and 3 Å. Product OX molecules were found to be rotationally excited and inverted with a mean rotational energy close to twice the value expected without angular momentum restrictions. The differences found between the calculated and the experimental angular distributions do not support any assumptions about osculating or short-lived complexes. The normal exoergicity ΔD₀ of 27 kJ/mol for the O + I₂ reaction agrees well with the experiments by Dunkin et al.     

UTa2O(S2)3Cl6: A ribbon structure containing a heterobimetallic 5d-5f M3 cluster

A new solid-state compound containing a heterobimetallic cluster of U and Ta, UTa₂O(S₂)₃Cl₆, has been synthesized and its structure has been characterized by single-crystal X-ray diffraction methods. UTa₂O(S₂)₃Cl₆ was synthesized from UCl₄ and Ta_1.2S₂ at 883 K. The O is believed to have originated in the Ta_1.2S₂ reactant. The compound crystallizes in the space group P1¯ of the triclinic system. The structure comprises a UTa₂ unit bridged by μ₂-S₂ and μ₃-O groups. Each Ta atom bonds to two μ₂-S₂, the μ₃-O, and two terminal Cl atoms. Each U atom bonds to two μ₂-S₂, the μ₃-O, and four Cl atoms. The Cl atoms bridge in pairs to neighboring U atoms to form a ribbon structure. The bond distances are normal and are consistent with formal oxidation states of +IV/+V/-II/-I/-I for U/Ta/O/S/Cl, respectively. The optical absorbance spectrum displays characteristic transition peaks near the absorption edge. Density functional theory was used to assign these peaks to transitions between S^1- valence-band states and empty U 5f-6d hybrid bands. Density-of-states analysis shows overlap between Ta 5d and U bands, consistent with metal-metal interactions.     

CO oxidation on MXene (Mo2CS2) supported single-atom catalyst: A termolecular Eley-Rideal mechanism

Finding transition metal catalysts for effective catalytic conversion of CO to CO₂ has attracted much attention. MXene as a new 2D layered material of early transition metal carbides, nitrides, and carbo-nitrides is a robust support for achoring metal atoms. In this study, the electronic structure, geometries, thermodynamic stability, and catalytic activity of MXene (Mo₂CS₂) supported single noble metal atoms (NM = Ru, Rh, Pd, Ir, Pt and Au) have been systematically examined using first-principles calculations and ab initio molecular dynamic (AIMD) simulations. First, AIMD simulations and phonon spectra demonstrate the dynamic and thermal stabilities of Mo₂CS₂ monolayer. Three likely reaction pathways, Langmuir-Hinshelwood (LH), Eley-Rideal (ER), and Termolecular Eley–Rideal (TER) for CO oxidation on the Ru₁- and Ir₁@Mo₂CS₂ SACs, have been studied in detail. It is found that CO oxidation mainly proceeds via the TER mechanism under mild reaction conditions. The corresponding rate-determining steps are the dissociation of the intermediate (OCO-Ru₁-OCO) and formation of OCO-Ir₁-OCO intermediate. The downshift d-band center of Ru₁- and Ir₁@Mo₂CS₂ help to enhance activity and improve catalytst stability. Moreover, a microkinetic study predicts a maximum CO oxidation rate of 4.01 × 10² s^-1 and 4.15 × 10³ s^-1 (298.15 K) following the TER pathway for the Ru₁- and Ir₁@Mo₂CS₂ catalysts, respectively. This work provides guideline for fabricating and designing highly efficient SACs with superb catalyts using MXene materials.     

Production of a spin-polarized,metastable He(23 S) beam for studies in atomic and surface physics

This beam was developed as a target for a crossed-beam electron-atom scattering experiment on the interaction of a polarized spin-1/2 electron with a polarized spin-1 atom. In the future this beam will be used in “Spin-Polarized Metastable Atom Deexcitation Spectroscopy” (SPMDS) for studying ferromagnetic surfaces without and with adsorbate layers. We use a discharge source for producing a beam of metastable helium atoms, a permanent sextupole magnet with a central stop at its exit for selecting He(2³ S) atoms in the Zeeman substatem _s =+1, a zero-field spin flipper for reversing the atomic beam polarization with respect to a magnetic guiding field, and a Stern-Gerlach magnet for analyzing the atomic polarization. At a distance of 90 cm beyond the exit of the sextupole, in the “interaction region” of an experiment, the polarized beam has a circular cross section of about 6 mm FWHM and a particle density of 1 · 10⁷ atoms/cm³. The reversible spin polarization was determined asP=0.90±0.02. A possible contamination of the beam with metastable singlet atoms is included within this value; the ground-state He atoms are not considered to be part of the polarized beam. An observed contamination with long-lived Rydberg atoms can easily be destroyed by applying a high electric field.     

Direct observation of the angular distribution of the chemiluminescence from Ba + N2O → BaO + N2

The angular distribution of the chemiluminescent reaction Ba + N₂O → BaO + N₂ has been investigated by photographing directly the chemiluminescence from this reaction in a crossed beam experiment. It was found that the lifetime of the reactively scattered chemiluminescent BaO molecules is sufficiently long (≈ 10^?s δ) to allow the observation of the angular distribution. From the dependence of this distribution on R and ? where R is the distance from the scattering center and ? the laboratory scattering angle, we conclude that under single collision conditions the chemiluminescence arises preferentially from highly excited vibrational-rotational levels of the A′¹ Π state of BaO.