Theoretical investigation of the Na+ + H2 system. III. Trajectory calculations of vibrationally inelastic collision processes

On the basis of an analytical potential energy surface for the electronic ground state of the Na⁺ + H₂ system reported recently, extensive trajectory calculations have been performed to study the collision dynamics of vibrationally inelastic processes at total energies up to ～3 eV. Special attention is given to the relative efficiacy of translational and rotational energy, respectively, in promoting vibrational energy transfer. Vibrational transitions are found to be substantially enhanced by initial molecular rotation. Furthermore, the applicability of simple models is discussed.     

Effect of rotation on vibrational excitation of H2 by Li impact

Coupled channel calculations of integral cross sections for rotational and vibrational excitation of H₂(X¹Σ⁺_g by collision with Li⁺ are reported for 1.2 eV in the c.m. system employing an ab initio potential energy surface and numerical vibration—rotation functions of the Koo?s—Wolniewicz potential function including adiabatic correction. Pure rotational excitation is found to strongly dominate the inelastic scattering occurring at this energy. Preparation of H₂ in various allowed non-zero rotational states is seen to enhance the 0 → 1 vibrational cross section by approximately an order of magnitude.     

Measurements of differential cross sections for vibrational quantum transitions in scattering of Li+ on H2

A pulsed monoenergetic ⁷Li⁺ ion beam (lab. energy 10–40 eV) is scattered from a highly collimated (= 1.5°) H₂ nozzle beam. The time-of-flight spectrum of the ions scattered in the forward laboratory direction shows both a fast peak corresponding to forward center-of-mass scattering and a slow peak corresponding to wide-angle center-of-mass scattering. These peaks have been further resolved to show contributions from individual vibrational quantum transitions. From an analysis of the time-of flight spectra the differential inelastic cross sections for a wide range of angles and energies between 2 eV <E_cm < 9 eV have been determined. The spectra also contain information on rotational inelastic cross sections.     

Microwave spectrum of propionyl chloride

The microwave spectrum of propionyl chloride has been investigated in the region 18.0–40.0 GHz, and transitions due to a cis conformer have been assigned. This form has a heavy atom planar configuration and the methyl group and the carbonyl oxygen atom are cis to each other. Using the substitution structures of propionic acid and acetyl chloride as molecular models for the propionyl chloride molecule, good agreement is found between observed and calculateò effective rotational constants. For the ³⁵Cl species satellite spectra assigned to the first four excited states of the C-C torsional mode have been observed together with the first excited state of the methyl torsional mode. The ground state spectrum has also been assigned for the ³⁷Cl species. Relative intensity measurements yielded the lowest C-C torsional vibration frequency of 86 ± 10 cm^?1. The CH₃ internal rotation frequency was found to be 197 cm^?1. Nuclear quadrupole coupling constants were determined for the ground state of the ³⁵Cl and ³⁷Cl species. From observed A-E splittings of ^bQ-branch transitions of the first excited state of the methyl torsional mode a barrier to internal rotation was estimated to be V₃ = 2480 ± 40 cal mol^?1 (867 ± 14 cm^?1).     

Measurements of inelastic cross sections for the (j,m) = (2,0)→(3,0) rotational transition of CsF in collisions with atoms and molecules

Individual state-to-state rotational transitions have been resolved in small angle scattering of polarized CsF molecules on Ne, Ar, C₂, H₆, N₂, CO, CO₂, CHF₃ at center of mass energies of about 0.1 eV. The absolute inelastic cross sections range from 5Ų up to 600Ų.     

Charge transfer shake-up satellites in X-ray photoelectron spectra of solid compounds of 3d0 ions

Satellite structure has been observed at 8 eV and 12 eV below the main metal 2p peaks for compounds of Sc³⁺ and Ti⁴⁺. These features are attributed to charge transfer “shake-up”: transitions (t_2g → t_2g^* and e_g → e_g^* respectively). The 8 eV satellites are only found in sulphate complexes of Sc³⁺. This is the first observation of satellites which are probably due to t_2g → t_2g^* monopole charge transfer transitions. The probability for this transition is usually low, resulting in the observation of satellites due to the e_g → e_g transition.     

Two-photon absorption spectroscopy of the Na2 molecule in the 4 eV region

By means of two-photon sequential absorption via real intermediate rotational levels of the A state, vibrational levels of three new excited electronic states of the sodium dimer have been observed in the 4 eV region. These states are identified as F¹ ∑⁺_g, G¹ Π_g and H¹ Π_g. Their vibrational and rotational constants have been determined.     

Close-coupling elastic and inelastic integral and differential cross sections for Li+ + H2 collisions

The quantum mechanical close-coupling formalism is applied to the study of elastic and rotationally inelastic Li⁺ + H₂ collisions making use of the Kutzelnigg-Staemmler-Hoheisel potential energy surface. Integral and differential cross sections for j = 0 → 0 and j = 0 → 2 are obtained in the collision energy range 0.2 to 0.9 eV and for j = 1 → 1 and j = 1 → 3 at 0.6 eV. A rainbow structure is observed in both the elastic and inelastic angular distributions and a quenching of the fast oscillations is found in the cross sections for j = 1 initially compared to the case j = 0 initially. At 0.6 eV. the calculated quantum mechanical angular distributions are compared to those from a classical trajectory calculation using the same surface and to the experimental ones. The dynamics of rotational excitation in the Li⁺ + H₂ system is contrasted to rotational excitation in systems for which the atom-diatom interaction is predominantly repulsive.     

Preparation and methane adsorption of two-dimensional carbide Ti<Subscript>2</Subscript>C

Here a novel material for methane adsorption was synthesized and studied, which is a graphene-like two-dimensional (2D) carbide (Ti₂C, a member of MXenes), formed by exfoliating Ti₂AlC powders in a solution of lithium fluoride (LiF) and hydrochloric acid (HCl) at 40 °C for 48 h. Based on first-principles calculation, theoretically perfect Ti₂C with O termination has a specific surface area (SSA) of 671 m² g^?1 and methane storage capacity is 22.9 wt%. Experimentally, 2.85 % exfoliated Ti₂C with mesopores shown methane capacity of 11.58 cm³ (STP: 0 °C, 1 bar) g^?1 (0.82 wt%) under 5 MPa and the SSA was 19.1 m² g^?1. For Ti₂C sample intercalated with NH₃·H₂O, the adsorbed amount was increased to 16.81 cm³ (STP) g^?1 at same temperature. At the temperature of 323 K, the adsorbed amount of as-prepared Ti₂C was increased to 52.76 cm³ (STP) g^?1. For fully exfoliated Ti₂C, the methane capacity was supposed to be 28.8 wt% or 1148 V (STP)v^?1. Ti₂C theoretically has much larger volume methane capacity than current methane storage materials, though its SSA is not very high.     

The first experimental observation of electronic transitions in C2+ and C2D+

High-resolution translational energy spectroscopy (up to 0.1 eV) has been carried out on 8 kV of C₂⁺ and C₂D⁺. The spetra obtained with C₂⁺ formed by different methods show considerable differences which are attributed to the formation of different spin states of the ion. Tentative assignments for the observed transitions have been made including one corresponding to excitation of the ⁴∑_g^? —X ⁴∑_g^? system, which may be useful as a probe of interstellar C₂⁺. Two broad transitions have been seen in the translational energy spectrum of C₂D⁺ which are in reasonable agreement with existing theoretical calculations. Tentative assignments are proposed for these transitions.     

Domain mobility and rotational tunnelling of hydrogen in graphite intercalates

The rotational tunnelling spectrum of hydrogen molecules adsorbed in the ternary intercalate C₂₄Cs(H_s)_x reveals the presence of at least four sorption sites whose occupancy changes with the degree of filling. The striking changes in the tunnelling spectrum at high filling are explained by the mobility of the caesium ions at 77 K and a reconstruction of the layer lattice.     

Anharmonicity in rotational and vibrational excitation of H2 by Li+ collisions

Integral cross sections for pure rotational and vibrational-rotational excitation of H₂(X¹Σ⁺_g) by Li⁺(¹S) impact are computed by close-coupling methods at 0.2, 0.6, and 1.2 eV in the c.m. system using vibrational functions that are numerical solutions of the one-dimensional radial Schrödinger equation for harmonic, Morse, and adiabatically corrected Kolos-Wolniewicz (KW) potential functions. Comparison of results employing KW and Morse functions shows excellent agreement for all transitions studied. Findings using harmonic oscillator functions, however, differ noticeably from KW and Morse values for vibrational (0 → 1) and very large rotational (Δj = 10) transitions, but are satisfactory for lower order (0 → 2, 4, 6, 8) rotational transitions.     

Vibrational structure in the photoelectron spectrum of O2+2Σg− (σg2s)

Discrete vibrational structure has been observed in the photoelectron spectrum of oxygen at an ionization potential of 40.33 eV. Two levels, attributed to the O₂⁺²Σ_g^?(σ_g2s) final state, have been detected with a vibrational spacing of 0.071 eV.     

The vacuum ultraviolet spectrum of stannane

The vacuum UV spectrum of SnH₄ has been recorded up to 110nm (12.26 eV). This spectrum has been interpreted by ab initio calculations (SCF + CI), using a relativistic pseudopotential to describe the core electrons of the tin atom. The spectrum consists of a broad band composed of three maxima (at 8.73, 9.53 and 11.33 eV). The transition below 9.50 eV have been attributed to transitions to diffuse Rydberg states (6s and 6p). The other bands are due essentially to valence transitions.     

Discussion of thermodynamic data obtained by adsorption gas chromatography of hydrocarbons on a new graphitized carbon black with a high specific surface area

Summary A new graphitized carbon black (Carbograph 5) with a specific surface area (560 m² g⁻¹) greater than those of commerically available graphitized carbons was studied by gas chromatography to determine the enthalpy, entropy, and free energy of adsorption of a series of alkanes (C₂−C₆). The adsorption properties were also investigated by considering changes in the isosteric heats and entropies of adsorption when a nonpolar stationary phase (squalane) was added to the adsorbent. The data obtained are discussed and compared with literature values for other graphitized carbon blacks.     

Low energy,variable angle electron-impact excitation of 1,3,5-hexatriene

A mixture of cis and trans 1,3,5-hexatriene has been studied by electron impact at incident electron energies of 20 eV, 40 eV, 50 eV, and 70 eV, at scattering angles from 0° to 80°, and with effective energy resolutions in the range from 0.05 eV to 0.15 eV. Singlet → triplet transitions with maximum intensities at 2.61 eV and 4.11 eV are observed. The lowest energy spin-allowed excitation which can be detected is the electric dipole-allowed $\text{X}$¹ A_g → 1 ¹B_u transition (in the notation appropriate for the trans isomer). No evidence has been found for a spin-allowed but symmetry-forbidden $\text{X}$¹ A_g → 2 ¹A_g excitation in the vicinity of 4.4 eV transition energy. Many other spin-allowed excitations are observed in the 6–11 eV energy-loss region, and the correlation between these features and those observed in high resolution ultraviolet absorption spectra and other electron-impact spectra is discussed.     

Discussion of thermodynamic data obtained by adsorption gas chromatography on carbograph 6

Summary Carbograph 6, a new graphitized carbon black with a specific surface area of 203 m² g⁻¹, as measured by BET, both uncoated and coated with up to 12% (w/w) of squalane, a non-polar stationary phase, has been studied by gas chromatographic determination of the enthalpy, entropy, and free energy of adsorption of a series of alkanes (C₂−C₆) and benzene. The data obtained are discussed and compared with those available in the literature for other graphitized carbon blacks. An example of a separation obtaned with Carbograph 6 is reported.     

甲烷在清洁 Pd(111) 及氧改性的 Pd(111) 表面解离的密度泛函理论研究

 采用广义梯度近似 (GGA) 的密度泛函理论 (DFT) 并结合平板模型, 研究了 CH4 在清洁 Pd(111) 及 O 改性的 Pd(111) 表面发生 C朒 键断裂的反应历程. 优化了裂解过程中反应物、过渡态和产物的几何构型, 获得了反应路径上各物种的吸附能及反应的活化能. 结果表明, CH4 采用一个 H 原子指向表面的构型在 Pd(111) 表面的顶位吸附, CH3 的最稳定的吸附位置为顶位, OH, O 和 H 的最稳定吸附位置均为面心立方. CH4 在清洁 Pd(111) 表面裂解的活化能为 0.97 eV, 低于它在 O 原子改性 (O 没有参与反应) 的 Pd(111) 表面的活化能 1.42 eV, 说明表面氧原子抑制了 CH4 中 C朒 键的断裂. 当亚表面 O 原子和表面 O 原子 (O 参与反应) 共同存在时, C朒 键断裂的活化能为 0.72 eV, 低于只有表层氧存在时的活化能 (1.43 eV), 说明亚表面的 O 原子对 CH4 分子的活化具有促进作用. CH4 在 O 原子改性的 Pd(111) 表面裂解生成 CH3 和 H, 以及生成 CH3 和 OH 的反应活化能分别为 1.42 和 1.43 eV, 说明 CH4 在 O 原子改性的 Pd(111) 表面发生这两种反应的难易程度相当.     

Formation of superoxide ions upon oxygen adsorption on magnesium-doped magnesium oxide: An EPR investigation

Oxygen adsorption on the surface of MgO, previously submitted to magnesium metal vapour, gives rise to the formation of at least five distinct species of adsorbed superoxide (O₂⁻) characterized by different g_zz values. Besides species previously observed on MgO, where O₂⁻ is generated by other methods, two new species are observed, having g_zz = 2.091 and g_zz = 2.064 respectively. The latter species is tightly bound to the surface and is assigned to O₂⁻ adsorbed on top of an array of five Mg²⁺ ions exposed because of the presence of an anion vacancy. The former is assigned to O₂⁻ weakly adsorbed on top of a five-coordinated Mg²⁺ ion at the (100) planar face of the oxide. This species differs from the other species present at the surface in that it is mobile and, as the temperature is raised from 77 to 298 K, exhibits rotation around the axis perpendicular to the surface. Spectra obtained by employing ¹⁷O-enriched O₂ indicate that both superoxide species are symmetrically adsorbed on the surface.     

Electronic band structure of solid CO2 as determined from the hv-dependence of photoelectron emission

Photoelectron energy distribution curves from solid CO₂ have been determined for excitation energies from hv = 14 up to 40 eV using synchrotron radiation. A 1:1 correspondence to the gas-phase photoelectron spectrum is observed for the occupied molecular orbitals. The vertical binding energies E_B^v (E_VAC = 0) and widths (fwhm) of the valence bands of solid CO₂ are determined to be 13.0 and 0.95 eV (1π_g); 16.7 and 1.1 eV (1π_u); 17.6 and 0.85 eV (3σ_u) and 18.8 and 0.8 eV (4σ_g) for the individual bands respectively. The partial photoemission cross sections differ importantly from those of the gas phase in exhibiting pronounced maxima at 5.2 eV (1π_g), 4.4–5.3 eV (1π_u + 3σ_u) and 4.2 eV (4σ_g) above the vacuum level, which is attributed to effects of high density of final (conduction-band) states. Further weaker maxima are observed at higher photon energies. Contrary to the case for the gas phase, the resonances are unperturbed in the solid by degenerate autoionizing molecular Rydberg states. The molecular origin of the resonances in the continuum is discussed and related to X-ray absorption spectra, electron-scattering data and to theoretical cross-section calculations. It is shown that the same set of resonances is observed in the different experiments. The resonances occur however at different energies due to different Coulomb interactions. The photoemission results presented provide also a key to the hitherto unexplained optical spectrum of solid CO₂ in the VUV range, making possible an assignment of the structures observed to Frenkel-type excitons (hv ≤ 15 eV) and interband transitions (hv ? 15 eV).