Electron transfer collisions between sulfur dioxide clusters and laser-excited Rydberg atoms

Electron attachment to SO₂ clusters is studied in a pulsed crossed beam apparatus, using laser-excited nf Rydberg atoms as a low energy electron source. The results are interpreted as an attachment to a dimer subcluster followed by a rapid impulsive dissociation of the nascent dimer anion. The remaining cluster anions possess a large amount of internal energy. At low principal quantum numbersn, the influence of the Rydberg ionic core leads to an important evaporation process interpreted with simple model calculations.     

Electron transfer from laser excited rydberg atoms to molecules. Absolute rate constants at low and intermediate principal quantum numbers

Using mass spectrometric detection of positive and negative ions, we have investigated ionizing reactions of Ne(ns,nd) Rydberg atoms, efficiently excited by resonant two-photon excitation of metastable Ne(3s ³ P ₂) atoms, with electron attaching moleculesBC (BC=SF₆, CCl₄, CS₂, O₂) at thermal collision energies. Absolute rate constants have been determined in the range of low and intermediate principal quantum numbersn(5≦n?30) by utilizing the photoionization signal caused by room temperature black-body radiation and the loss of Ne(3s ³ P ₂) atoms, associated with the laser excitation. Substantially differentn-dependences of the electron transfer cross section have been found for the larger molecules (BC = SF₆, CCl₄) and the smaller molecules (BC = CS₂, O₂). Simple model calculations have been performed to gain new insight into the dynamics of the electron transfer process; forBC = SF₆, our results at lown(5 ≦n ≦ 10) suggest that internal energy conversion in the Coulombic complex Ne⁺ — SF ₆ ^? is important for the formation of the detected ions.     

Crystal structure of a new molecular complex of fullerene with tetramethyltetraselenafulvalene: C60·TMTSF·2CS2

A new molecular complex of fullerene with tetramethyltetraselenafulvalene (TMTSF), C₆₀·TMTSF·2CS₂, (1) was synthesized. The structure and composition of the complex were established by X-ray diffraction analysis. The crystals of C₆₀·C₁₀H₁₂Se₄·2CS₂ are monoclinic:a=15.407(2),b=12.934(2),c=12.026(2) Å β=108.39(3)°,V=2274.1(6) ų, space groupCm, Z=2,d _calc=1.929 g cm^?3,R=0.047. The crystal structure of 1 consists of layers. Layers formed by fullerene and CS₂ molecules alternate with layers of TMTSF molecules. Peculiarities of the crystal structure of 1 are the nonplanar conformation of TMTSF molecules and the absence of shortened C…C contacts between adjacent fullerenes molecules. The energy of intermolecular TMTSF…C₆₀ interactions in the crystal was estimated.     

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.     

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).     

Dissociation patterns in N2O following electron impact

A number of dissociation channels in N₂0 have been observed by time-of-flight spectroscopy following electron impact excitation. The metastable atoms and molecules produced were directly detected. Excited N₂ molecules were produced in the A³Σ_u⁺, B³Π_g and B′³Σ_u^? states in conjunction with ground state oxygen atoms. A number of additional dissociation channels were monitored by observing the production of oxygen and nitrogen atoms in Rydberg states. The results indicate the existence of potential minima in some of the repulsive surfaces involved.     

Photochemistry of CS2/Cl complexes—combined pulse radiolysis–laser flash photolysis studies

Complexes of chlorine atoms and carbon disulfide (CS₂) were produced by pulse radiolysis of CS₂ in halocarbons and photochemical reactions were studied by laser flash photolysis. Excitation of CS₂/Cl complexes resulted in rapid and permanent photobleaching. The photobleaching of CS₂/Cl complexes is due to intermolecular chlorine atom abstraction in CCl₄ with a quantum yield of 0.04, while that ascribed to hydrogen atom abstraction in 1,2-dichloroethane has a quantum yield of 0.21. The effects of additives are discussed based on the bond dissociation energy.     

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.     

Ab Initio Study on the Stability of NgnBe2N2, NgnBe3N2 and NgBeSiN2 Clusters

The global minima of Be₂N₂, Be₃N₂ and BeSiN₂ clusters are identified using a modified stochastic kick methodology. The structure, stability and bonding nature of these clusters bound to noble gas (Ng) atoms are studied at the MP2/def2‐QZVPPD level of theory. Positive Be?Ng bond dissociation energy, which gradually increases down Group 18 from He to Rn, indicates the bound nature of Ng atoms. All of the Ng‐binding processes are exothermic in nature. The Xe and Rn binding to Be₂N₂ and Be₃N₂ clusters and Ar?Rn binding to BeSiN₂ are exergonic processes at room temperature; however, for the lighter Ng atoms, lower temperatures are needed. Natural population analysis, Wiberg bond index computations, electron density analysis, and energy decomposition analysis are performed to better understand the nature of Be?Ng bonds.     

Cationic Rydberg states observed in resonantly enhanced electron spectra of CS2

The inner valence electron spectrum of the CS₂ molecule has been investigated in the binding energy range between 18.6 and 26.3 eV using synchrotron radiation for ionisation. Photon energies in the range from 67 to about 167 eV have been used, with particular focus on 166.70, 166.89 and 167.09 eV for which S2p electrons are resonantly transferred into Rydberg orbitals close to the ionisation threshold. From there, autoionisation takes the molecule into various cationic states characterized by two valence holes and a Rydberg spectator electron. Many new bands are observed which contain vibrational progressions with spacings around 120 meV in most cases. These are assigned as excitations of the totally symmetric stretching ν₁ mode in the cationic state. The new bands reflect states in the cation that are close to the electronic states of the dication and assignments are made by comparison to double ionisation electron spectra.     

Negative ion mass spectra of metal complexes: Secondary electron capture and CS2 elimination from nickel (ii) dithiocarbamates

Negative ion mass spectra of series of bis-(N, N-dithiocarbamato)nickel(II) complexes of formula [NiS₂C·NR¹R²]₂ (where·NR¹R² ? ·NEt₂ ·NPr₂, ·NBu₂, pyrrolidinyl, piperidyl, morpholinyl, and ·NEtPh) have been obtained by secondary electron capture. Intense molecular anions are given for all compounds, with most fragments originating from these ions. Metastable data indicate that CS₂ is eliminated from all molecular anions.     

Molecular rydberg transitions in carbon monoxide: term value/ionization energy correlation of BF,CO and N2

The linear correlation between the term value and ionization energy for molecular Rydberg transitions is tested for the sequence of isoelectronic molecules BF, CO and N₂ based on a new measurement of the absorption spectrum of CO and data for BF and N₂. For the npσ series and npπ series converging on the first ionization potential, we find an excellent linear behavior (within 10 meV) corroborating (i) the correlation and (ii) the individual assignments. For Rydberg series leading to the A ²Π and B ²Σ⁺ states, where no data for BF are available, a comparison of term values for CO and N₂ is presented.     

Charge‐transfer‐to‐solvent absorption spectra of I−(H2O)3–5 at a finite temperature via simulation

Ground‐state equilibrium Born–Oppenheimer molecular dynamics on I^?(H₂O)_3–5 clusters at ～200 K are performed to sample configurations for calculating the charge‐transfer‐to‐solvent (CTTS) absorption spectra for these clusters. When there are more water molecules in clusters, the calculated CTTS spectra are found to become more intense with the absorption maxima shifting to higher energies, which is in agreement with experimental results. In addition, compared with the findings for optimized structures, the absorption energies of the iodide 5p orbitals are red‐shifted at ～200 K because, on average, the distances between the iodide and the dangling hydrogen atoms are increased at finite temperatures which weakens the interactions between the iodide and water molecules in the clusters. Moreover, the number of ionic hydrogen bonds in the clusters are also reduced. However, it is found that all dangling hydrogen atoms must be considered to obtain a good correlation between the CTTS excitation energy and the average distance between the iodide and the dangling hydrogen atoms, which indicates the existence of the strong interactions of the CTTS electron with all of the dangling hydrogen atoms.     

Effective absolute rate constant for the formation of negatively-charged CO2 cluster ions by electron transfer from state-selected Rydberg atoms

We have studied electron transfer from state-selected Ar** (nd) Rydberg atoms to (CO₂) _m clusters for 12≦n≦48. The relative rate constant for the total negative ion formation reaches its maximum forn=21 and decreases towards lower and highern. From an accurate study of Penning ionization of nozzle beams with and without cluster formation we were able to derive the condensed fraction in our (CO₂) _m cluster beam and from a statistical analysis of cluster distributions we obtain an estimate for the absolute value of the effective rate constant for the total negative ion formation, which amounts to (4.5 ± 3) · 10^?8 cm³/s for Ar** (21d).     

Pseudo-spectral dipole oscillator-strength distributions for SO2, CS2 and OCS and values of some related dipole—dipole and triple-dipole dispersion energy constants

Pseudo-spectral dipole oscillator strengths and excitation energies, which are discrete representations of the original continuous dipole oscillator-strength distributions (DOSDs), are presented for the ground-state SO₂, CS₂ and OCS molecules. These pseudo-DOSDs, together with previously published pseudo-DOSDs, are used to evaluate the dipole—dipole and triple-dipole dispersion-energy coefficients for all the two- and three-body interactions between SO₂, CS₂ and OCS and between these molecules and H₂, N₂, O₂, NO, N₂O, H₂O, NH₃, CO, CO₂, CH₄, C₂H₆, C₄H₁₀ and C₆H₁₄, with an estimated uncertainty of 1–2%. The importance of results of this type is discussed briefly.     

Lie algebraic approach to Fermi resonance levels of CS2 and CO2

By using the general Hamiltonian based on the Lie algebraic method, the highly excited vibrational energy levels of linear triatomic molecules CS₂ and CO₂ are calculated, which proves that neglecting other perturbations and considering only 1:2 Fermi resonance, the obtained Hamiltonian can be used effectively to calculate the vibrational energy levels of linear triatomic molecules. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 81: 154–161, 2001     

Comprehensive Mechanism of CO2 Electroreduction on Non-Noble Metal Single-Atom Catalysts of Mo2CS2-MXene

In this work, a series of non-noble metal single-atom catalysts of Mo₂CS₂-MXene for CO₂ reduction were systematically investigated by well-defined density-functional-theory (DFT) calculations. It is found that nine types of transitional metal (TM) supported Mo₂CS₂ (TM-Mo₂CS₂) are very stable, while eight can effectively inhibit the competitive hydrogen evolution reaction (HER). After comprehensively comparing the changes of free energy for each pathway in CO₂ reduction reaction (CO₂RR), it is found that the products of TM-Mo₂CS₂ are not completely CH₄. Furthermore, Cr-, Fe-, Co- and Ni-Mo₂CS₂ are found to render excellent CO₂RR catalytic activity, and their limiting potentials are in the range of 0.245–0.304 V. In particular, Fe-Mo₂CS₂ with a nitrogenase-like structure has the lowest limiting potential and the highest electrocatalytic activity. Ab initio molecular dynamics (AIMD) simulations have also proven that these kinds of single-atom catalysts with robust performance could exist stably at room temperature. Therefore, these single TM atoms anchored on the surface of MXenes can be profiled as a promising catalyst for the electrochemical reduction of CO₂.     

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.     

Solvent effects in thermal electron attachment to clusters containing molecular oxygen

Thermal electron attachment to oxygen is strongly modified when this molecule is bound in heterogenous van der Waals clusters. With the help of a laser-excited Rydberg electron source, we investigate the influence upon electron capture of the solvent nature by comparing O₂(H₂O)_N and O₂(C₆H₆)_N attachment rate constants, and we observe size effects down to nearly zero energy.     

Electron transfer from state-selected Rydberg atoms to (N2O) m and (CF3Cl) m clusters

Electron transfer from state-selected Ar** (ns, nd) Rydberg atoms to neutral (N₂O) _m and (CF₃Cl) _m clusters has been studied for principal quantum numbersn between 10 and 45. The dominant product ions are (N₂O) _q ·O^? and, dependent on stagnation pressure, (CF₃Cl) _q ·Cl^? or (CF₃Cl) _q ·FCl^?, respectively. In both cases we observe a strongn-dependence of the negative cluster ion spectra. While for lown, broad ion distributions are observed, much narrower distributions are found for highn, especially for N₂O negative cluster ions around the dominant species (N₂O)₆·O^?, corresponding to a remarkably size-selective process. Possible reasons for this behaviour are briefly discussed.