Collision-induced intramolecular vibration—vibration energy transfer in CO2: CO2(0001) + H2/D2

Intramolecular vibration—vibration energy transfer cross sections have been calculated for CO₂(00⁰1) + H₂/D₂ → CO₂(11¹0) + H₂/D₂, → CO₂(10⁰0) + H₂/D₂, and → CO₂(20⁰0) + H₂/D₂ based on the mechanism that the energy mismatch is transferred to the translational motion. For CO₂ + H₂, the calculated cross section for CO₂(00⁰1) + H₂ → CO₂(10⁰0) + H₂ is in good agreement with experimental data. Cross sections for the processes (00⁰1 → 11¹O) and (00⁰1 → 20⁰0) are found to be too small compared with experimental data. For CO₂ + D₂, (00⁰1 → 10⁰0) is also the most important process and appears to represent experimental data at room temperature. The sum of three cross sections of CO₂ + H₂ is always greater than that of CO₂ + D₂ over the temperature range of 100–2500 K.     

Temperature dependence of the probabilities of VV energy exchange between H2 and DCl

The temperature dependence of the removal of the vibrational energy of H₂ by DCl in H₂(1) + DCl(0) has been investigated over the range of 300–3000 K. The energy transfer probability of H₂(1) + DCl(0) → H₂(0) + DCl(1), where the vibrational energy of H₂(1) is removed by both the vibrational and rotational motions of DCl(0), is found to be strongly temperature dependent and increases with temperature closely following the relation log P α T^1/3. Over the temperature range it changes by two orders of magnitude. The probability of the near-resonant process H₂ (1) + DCl(O) → H₂(0) + DCl(2) is very close to that of the former at 300 K, but it increases only slightly as the temperature is raised to 3000 K. The sum of the probabilities of these two processes at 300 K is 3.4 × 10^?5, which agrees with the experimental value of 3.95 × 10^?5.     

Deactivation of CO2(00o1) by some polyatomic molecules

The rates of collisional deactivation of CO₂(00^o1) by formic acid, acetic acid, ethylene oxide and acetaldehyde were measured using the laser-induced fluorescence technique. We found that K_CO2-HCOOH = 140 ± 22 ms^?1 Torr^?1 at 400 K, K_CO2-CH₃COOH varied from 156± 33 to 45.8 ± 26.7 ms^?1 Ton^?1 as the temperature was changed from 500 to 750 K, K_CO2-C₂H₄O varied from 101 ± 33 to 55.5 ± 7.3 and K_CO2-CH₃CHO from 48.6 ± 10.7 to 26.5 ± 4.9 ms^?1 Torr^? in the temperature range 300–650 K.     

Vibrational relaxation of CO2(0001) in pure CO2

The rate constant for collisional deactivation of CO₂(00⁰1) in pure CO₂ has been measured at room temperature using the laser fluorescence technique. The relaxation rate has been found to be (1.0 ± 0.2) × 10^?14 cm³ s^?1 which is in favorable agreement with previously published values.     

Basis-set effects in quantum-mechanical calculations of translational-to-vibrational energy transfer in O(3P) + CO2 collisions

Cross sections for the vibrational excitation of CO₂ in collisions with O(³P) from the ground state to the (00⁰1) state are computed using vibrational-close-coupling with the infinite-order-sudden approximation for rotation (VCC IOS). For a relative translational energy of 3 eV, several vibrational basis sets are tested for convergence of this cross section. Using the best converged vibrational basis set for 3 eV, the (00⁰1) → (00⁰1) cross section is computed over the relative translational energy range of 2 to 6 eV. Previous discrepancies of factors of 2 to 7 between the VCC IOS method and quasiclassical trajectory studies are reduced to factors of 1.1 to 2.5.     

Photodissociation of O2+(H2O)

The photodissociation cross section of the weakly bound positive ion cluster O₂⁺(H₂O) has been measured at 15 discrete energies between 1.833 and 2.727 eV. Measurements indicate the cross section increases smoothly from 0.6 to 6 × 10^-18 cm² over this energy range. These cross section values are the largest reported for a positive ion cluster of atmospheric importance.     

CH2(1A1) from CH2N2 photolyses at 4358 and 3660 Å vibrational energy distributions upon reaction with cyclobutane

Approximate vibrational energy distribution for CH^*₂(¹A₁) from diazomethane photolyses at 4358 and 3660 Å have been determined to be reasonably broad. These distributions apply to CH^*₂(¹A₁) at the time of reaction with cyclobutane and were deduced from the internal energy distribution of the formed chemically activated methylcyclobutane. An apparent anomaly in the pressure dependence of the decompositions of CH₂(¹A₁) generated chemically molecules is explained. The anomaly pertains to the relative behavior of systems utilizing ketene and diazomethane photolyses as CH₂(¹A₁) sources. The explanation offered is that the vibrational energy distributions for CH^*₂(¹A₁) are narrow for ketene photolyses at 3340 or 3130 Å and broad for diazomethane photolyses at 4358 or 3660 Å.     

Study of energy transfer from laser excited CO2 to chloromethanes

Collisional energy transfer from CO₂(ν₃) to chloromethanes was studied in the temperature range 300–700 K using the laser induced fluoresce technique. Theoretical calculations using SSH and SB theories were carried out to identify the CO₂(ν₃) deactivation process. The experimental probabilities were found to decrease linearly with increasing number of substituted chlorine atoms.     

The charge transfer reactions of protons with carbon dioxide: A two-state treatment

Although the dissociative electron transfer reactions between protons and carbon dioxide are endothermic by 0.19–9.1 eV, the reactions have a large total cross section at low keV collision energies. The results are quantitatively modelled in terms of the modified Strueckelberg-Demkov mechanism for the non-crossing of reactant and product diabatic potential energy curves. Charge transfer to give the ground state of CO⁺₂ occurs at 4.05–4.26 Å. The H atom and CO⁺₂ formed may then suffer a non-crossing excitation at 1.6–2.1 Å during the evolution of a single-collision event, to produce the excited CO⁺₂. The experimental results cannot be interpreted by a curve crossing mechanism of the Landau-Zener type.     

Ion pair formation in alkali-SF6 collisions: Dependence on collisional and vibrational energy

The dependence of ion pair formation in collisions of fast alkali atoms (K, Na and Li) with SF₆ on the initial relative kinetic energy and the internal energy of the target molecule has been studied by the crossed molecular beam method. Using a mass spectrometer we have measured total cross sections for negative ion formation as a function of translational and internal energy. Collision energies ranged from threshold up to 35 eV and SF₆ source temperatures were varied from 300 K to 850 K.By means of an inverse Laplace transform of the measured cross sections, we have determined total specific cross sections for each negative ion depending on the SF₆ vibrational energy and at fixed relative kinetic energy.The relative importance of both collisional and internal energy in promoting the electron transfer process is discussed for the various reaction channels in terms of a collision model. An essential feature of this model is the stretching of the S-F molecular ion bond during the collision. The product show complete relaxation in the threshold region, i.e., vibrational and collisional energy are equivalent: This holds for the SF⁻₆ formation only near threshold and for the SF⁻₅ and F⁻ formation up to about 2 eV above threshold. In the post-threshold region the effect of the internal energy on the cross section dominates over that of the translational energy.From these measurements the adiabatic electron affinity of SF₆ is inferred to be 0.32 ± 0.15 eV, T = 0 K. Some other thermodynamic data are deduced: EA(SF₅) > 2.9 ± 0.1 eV (T = 300 K) and D₀(SF⁻₅-F) = 1.0 ± 0.1 eV.     

Temperature dependence of the vibration-vibration transfer rates from CO2 and N2O excited in the (0001) vibrational level to 14N2 and 15N2 molecules

V-V transfer rates from CO₂ and N₂O excited in the (00⁰1) vibrational level to ¹⁴N₂ and ¹⁵N₂ are determined from 150 to 1200 K using the laser fluorescence method, and compared with values calculated on the basis of dipole-quadrupole interactions.     

Charge transfer collisions between fullerenes: C 60 3+ + C60

Charge transfer collisions between C ₆₀ ³⁺ and C₆₀ are studied for collision energies between 400 and 3600 eV. Single and double electron transfers are observed, both occuring under single collision conditions. Absolute charge transfer cross sections are determined as a function of collision energy. The cross section for single electron capture of approx. 300 Ų is about two times larger than that for double electron transfer. For both processes the cross section increases slightly with increasing collision energy.     

In Situ Investigation of Methane Dry Reforming on Metal/Ceria(111) Surfaces: Metal–Support Interactions and C−H Bond Activation at Low Temperature

Studies with a series of metal/ceria(111) (metal=Co, Ni, Cu; ceria=CeO₂) surfaces indicate that metal–oxide interactions can play a very important role for the activation of methane and its reforming with CO₂ at relatively low temperatures (600–700 K). Among the systems examined, Co/CeO₂(111) exhibits the best performance and Cu/CeO₂(111) has negligible activity. Experiments using ambient pressure X‐ray photoelectron spectroscopy indicate that methane dissociates on Co/CeO₂(111) at temperatures as low as 300 K—generating CH_x and CO_x species on the catalyst surface. The results of density functional calculations show a reduction in the methane activation barrier from 1.07 eV on Co(0001) to 0.87 eV on Co²⁺/CeO₂(111), and to only 0.05 eV on Co⁰/CeO_2−x (111). At 700 K, under methane dry reforming conditions, CO₂ dissociates on the oxide surface and a catalytic cycle is established without coke deposition. A significant part of the CH_x formed on the Co⁰/CeO_2−x (111) catalyst recombines to yield ethane or ethylene.     

Photodissociation of the dimer ions Ar+2, Ne+2, and (CO2)+2

The tandem quadrupole photodissociation mass spectrometer has been used to study photodissociation reactions of Ar⁺₂, Ne⁺₂, and (CO₂)⁺₂. The cross sections for photodissociation of Ar⁺₂ exhibited a strong dependence on ion source pressure, varying from 2 × 10 ^?18cm² at 0.1 torr to 6 × 10^?19cm² at 0.5 torr. A large photodissociation cross section (2 × 10^?17cm² for the reaction (CO₂)⁺₂ → CO⁺₂+ CO₂ was observed at the red end of the visible spectrum (580–620 nm) suggesting that this may be an important reaction in CO₂ rich planetary ionspheres such as that of Mars.     

Structures isomorphes MeX2O4—Evolution structurale entre 2 K et 300 K de l'antimonite FeSb2O4: Elasticité et ordre magnétique anisotropes

Neutron diffraction has been used to study the whole structural evolution of the antimony oxide FeSb₂O₄, from 2 to 300 K. The antiferromagnetic order has been investigated: at 2 K the magnetic moment is M = 3.8 μ_B. An extrapolated Néel temperature T_N = 45 ± 6 K is observed. The function M(T) below T_N is similar to that found in the isomorphous NiSb₂O₄. Magnetostrictive effects are observed. Above 70 K, the thermal expansion tensor is anisotropic with α_a ? α_c. Using the anisotropic temperature factors B_a (Ų), B_c (Ų) at 2 and 300 K, anisotropic Debye temperatures are calculated. Then, using simple approximations, mean force constants F_a, F_c are calculated; they allow to evaluate the anisotropic compressibility coefficients χ_a ～ 0.857 × 10^?11Pa^?1, χ_c ～ 0.467 × 10^?11Pa^?1; the value of the Grüneisen constant is $\text{γ}\text{= 0.33}$.     

Structural aspects of the metal-insulator transitions in V0.985Al0.015O2

The crystal structure of V_0.985Al_0.015O₂ has been refined from single-crystal X-ray data at four temperatures. At 373°K it has the tetragonal rutile structure. At 323°K, which is below the first metal-insulator transition, it has the monoclinic M₂ structure, where half of the vanadium atoms are paired with alternating short (2.540 Å) and long (3.261 Å) V-V separations. The other half of the vanadium atoms form equally spaced (2.935 Å) zigzag V chains. At 298°K, which is below the second electric and magnetic transition, V_0.985Al_0.015O₂ has the triclinic T structure where both vanadium chains contain V-V bonds, V(1)-V(1) = 2.547 Å and V(2)-V(2) = 2.819 Å. At 173°K the pairing of the V(1) chain remains constant: V(1)-V(1) = 2.545 Å, whereas that of the V(2) chain decreases: V(2)-V(2) = 2.747 Å. From the variation of the lattice parameters as a function of temperature it seems that these two short V-V distances will not become equal at lower temperatures. The effective charges as calculated from the bond strengths at 298 and 173°K show that a cation disproportionation has taken place between these two temperatures. About 20% of the V⁴⁺ cations of the V(1) chains have become V³⁺ and correspondingly 20% of the V⁴⁺ cations of the V(2) chains have become V⁵⁺. This disproportionation process would explain the difference between the two short V-V distances. Also it would explain why the T → M₁ transition does not take at lower temperatures.     

Excitation of alkali atoms in collisions with molecules. Population of the states K(62S) and K(52-P)

Radiation at 4050 and 6930 A has been observed in collisions of fast potassium atoms with N₂, O₂, CO, NO, CO₂, C₂H₄ and C₆H₆. Emission at both wavelengths is weak compared to that at 7680 Å. The threshold energy for emission at 6930 Å has been found to be equal to the excitation energy (3.4 eV) of the state K(6²S) for N₂ and NO, but higher (5.5 eV) for CO.     

Vibrational energy transfer from N2 to CO on electron excitation of N2-CO solids at 4.2 K

Spectra emitted from 0.1% CO-N₂ solids excited with high energy electrons at 4 K show evidence for resonant transfer of vibrational energy from highly excited vibrational levels of N₂ to CO in the process N₂(X¹Σ_g⁺, ν) + CO(ν = 0) → N₂(X¹Σ_g⁺, ν - 1) + CO(ν = 1) + phonons. Energy transfer from levels with ν ? 9 has been observed.     

A study of the formation of LiNbO3 in the system Li2CO3Nb2O5

The formation process of LiNbO₃ in the system Li₂CO₃Nb₂O₅ was discussed from the results of non-isothermal or isothermal TG experiments and X-ray analysis. The mixture Li₂CO₃ and Nb₂O₅ in mole ratios of 1:3, 1:1 or 3:1 was heated at a rate of 5°C min^?1 or at various temperatures fixed in the range 475 to 677°C. If the system has a composition of Li₂CO₃ + 3Nb₂O₅ or 3Li₂CO₃ + Nb₂O₅, the reaction between Li₂CO₃ and Nb₂O₅ proceeds with CO₂ evolution to form LiNbO₃ at ca. 300–600°C, but Nb₂O₅ or Li₂CO₃ remains unreacted. A composition of Li₂CO₃ + Nb₂O₅ gives LiNbO₃ at 300–700°C. The diffusion of Li₂O through the layer of LiNbO₃ is rate-controlling with an activation energy of 51 kcal mol^?1. The reaction between LiNbO₃ and Nb₂O₅ gives LiNb₃O₈ at 600–700°C. At 700–800°C, a slight formation of Li₃NbO₄ occurs by the reaction between LiNbO₃ and Li₂O at the outer surface of LiNbO₃ and the Li₂O component of Li₃NbO₄ diffuses toward the boundary of the LiNb₃O₈ layer through the LiNbO₃ layer. The single phase of LiNbO₃ is formed above 850°C.     

Excited state dynamics of the11BO2 free radical

The excitation spectrum of the double-headed 00°0-00°0 band of BO₂ (A²Π_u-X²Π_g) was recorded by LIF. Special attention was paid to determine the dependence of the radiative lifetime of (00°0) A²Π state with J and the quenching by bath gases N₂, Ar, O₂. The determinations of fluorescence decay were made in real time. The mean radiative lifetime τ_r of the A²Π_3/2(00°0) state of ¹¹ BO₂ was determined to be 91 ± 4 ns (1σ).