Angular dependence of rotational and vibrational energies of product CO2 in CO oxidation on Pd(110)

The rotational and vibrational energies of product CO(2) in the CO oxidation on Pd(110) surfaces were measured as functions of desorption angles. The antisymmetric vibrational temperature (T(a)) was separately determined from the other vibrational modes from the normalized chemiluminescence intensity. The rotational temperature (T(rot)) and vibrational temperature averaged over the symmetric and bending modes (T(sb)) were then determined by the position and width of spectra by comparison with simulated spectra. On Pd(110)-(1x1), with increases in the desorption angle, T(a), T(sb) and T(rot) decreased in the [001] direction but remained constant in [11[combining macron]0]. However, such anisotropy disappeared when the ratio of exposure of O(2) to that of CO decreased, resulting in a gradual decrease of the three temperatures with increases in the desorption angle. On Pd(110) with missing rows, the three temperatures increased in [001] but decreased in [11[combining macron]0], indicating that the transition state changes with the geometry of the substrate. On Pd(110) with missing rows, T(a) was significantly lower than T(sb), although T(a) was close to or higher than T(sb) on Pd(110)-(1x1). However, there was no significant difference in the angular dependence between T(a), T(sb) and T(rot).     

Time-resolved studies of state-to-state vibrational energy transfer: I2(B3IIou+:v′ = 19) + He

This paper presents an experimental procedure to study state-to-state collisional dynamics by using tunable and pulsed laser techniques and time-resolved and dispersed fluorescence methods. For the first time, the decay processes of electronically excited iodine, B³II_ou⁺ (v′ = 19), to the adjacent vibrational states in collisions with He molecules have been directly observed in real time. The rate constants for the state-to-state vibrational energy transfer obtained are, k,_vHe(19→18) = (2.76±0.05)x10^?11cm³s^?1 molecule^?1 and k_vHe(19→20) = (1.65±0.04) × 10^?11 cm³s^?1 molecule^?1. These results are in satisfactory agreement with the detailed balance principle.     

Association reactions with state selected ions at meV collision energies: CO+ (v=0,j) + 2 CO → (CO) 2 + +CO

Relative three-body association rate coefficients for the title reaction have been measured as a function of the rotational statej of the CO⁺ ion at collision energies below 1 meV. A significant decrease of the dimer formation has been observed whenj increases from 0 to 7 (E _rot=0?13.7 meV). Multiphoton ionization (MPI) is used to create the ions in the high pressure region of a pulsed supersonic expansion of pure CO. This method allows both the rather precise determination of the rotational population of the neutrals (〈E _rot〉 ～1.5 meV) and the preparation of the ions exclusively in the vibrational ground state and in well defined rotational states. Due to its very steep energy dependence the ternary association reaction can be “switched off” within a few tenths of a millimeter using an acceleration field of 1–3 V/cm. The short effective interaction time of less than 250 ns leads to almost single collision conditions. i.e. we perform state selective studies. The kinetics and kinematics (mean kinetic energy, competition between relaxation and association) are analyzed numerically. A consistent picture results from the assumption that the ternary rate coefficient depends only on the total energy of the complex irrespective of whether its origin is rotation or translation.     

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.     

New results for the OH (nu = 0,j = 0) + CO (nu = 0,j = 0) --> H + CO2 reaction: Five- and full-dimensional quantum dynamical study on several potential energy surfaces

Full- [six-dimensional (6-D)] and reduced-dimensional [five-dimensional (5-D)] quantum wave packet calculations have been performed for the title reaction to obtain reaction probabilities deriving from the ground rovibrational states of OH and CO with total angular momentum J = 0. Three potential energy surfaces (PES) are studied, namely, those of Bradley and Schatz (BS), Yu, Muckerman, and Sears (YMS), and Lakin, Troya, Schatz, and Harding (LTSH). 6-D calculations are performed only for the BS PES, while 5-D results are reported for all three PES'. The 6-D results obtained in the present work improve on those previously reported, since a larger vibrational basis and a better representation of the OH and CO bonds has been introduced. In particular, we now employ a generalized Lanczos-Morse discrete variable representation for both the OH and CO vibrations. In a further improvement, the generalized discrete variable representation of the CO vibration is based on different CO intramolecular potentials for the asymptotic and product grids employed in our projection formalism. This new treatment of the vibrational bases allows for a large reduction in computation time with respect to our previous implementation of the wave packet method, for a given level of accuracy. As a result, we have been able to extend the range of collision energies for which we can obtain converged 6-D results to a higher energy (0.8 eV) than was possible before (0.5 eV). The comparison of the new 6-D and previous 5-D results for the BS PES shows good agreement of the general trend in the reaction probabilities over all collision energies considered (0.1-0.8 eV), while our previous 6-D calculation showed reaction probabilities that differed from the 5-D results by up to 10% between 0.5 and 0.8 eV. The 5-D reaction probabilities reveal interesting trends for the different PES'. In particular, at low energies (< 0.2 eV) the LTSH PES gives rise to much larger reactivity than the other PES', while at high energies (> 0.3 eV) its reaction probability decreases with respect to the BS and YMS PES', being more than a factor of 2 smaller at 0.8 eV. A 5-D calculation on a modified version of the LTSH surface shows that the van der Waals interaction in the entrance channel, which is not correctly described in the other PES' is largely responsible for its larger reactivity at low energies. The large difference between the 5-D reaction probabilities for the YMS and LTSH PES' serves to emphasize the importance of the van der Waals interaction for the reactivity at low energies, because most of the stationary point energies on the YMS and LTSH PES are rather similar, being in line with high-level ab initio information.     

Laser studies of vibrational energy transfer and relaxation of CO trapped in solid neon and argon

The infrared emission of CO trapped in solid Ne and Ar is observed at low temperature. The first vibrational level of ¹²C¹⁶O is excited by a Q-switched frequency doubled CO₂ laser. The emission spectrum consists of several lines arising from upper vibrational levels of ¹²C¹⁶O and also of ¹³C¹⁶O and ¹²C¹⁸O which are present in natural abundance. An interpretation is proposed which is based on the assumption that long range dipole—dipole interaction is the main physical process involved in these experiments. Resonance energy transfer produces an energy migration among ¹²C¹⁶O molecules without any change in vibrational populations. Phonon assisted energy transfer takes place between vibrational levels of the various isotopic species present in the solution. In order to satisfy the resonance condition a phonon is emitted or absorbed whose energy compensates for the energy mismatch between the transitions in each interacting molecule due to isotopic effect and or vibrational anharmonicity. The range of this process is greatly extended by energy migration. At the low phonon bath temperature phonon emission is much more probable than phonon absorption. So a strong excitation of upper vibrational levels with in some cases population inversions is observed.Molecular impurities act as efficient quenching centers even at very low concentration. When highly purified samples are used, the fluorescence decay time is found to be 20.6 ms in Ne and 14.5 ms in Ar and does not significantly depend upon concentration and temperature. It is concluded that radiationless relaxation is unimportant.     

Electronic-to-vibrational energy transfer reactions: Na(3 2P) + CO (X1Σ+, υ=0)

The vibrational distribution of CO produced from the electronic-to-vibrational energy transfer reaction: Na(3²P) + CO(X¹Σ⁺, υ=0)→Na(3²S) + CO(X¹Σ⁺, υ?8) has been determined by means of infrared resonance absorption measurements employing a cw CO laser. A flash-lamp-pumped dye laser is used to excite the ground state Na to the 3²P_{$\text{1}\text{2}$} and 3²P_{$\text{3}\text{2}$} states. The CO molecules formed in the reaction were found to be vibrationally excited up to the limits of available electronic energies carried by the excited Na atoms, and the vibrational population exhibits a maximum at υ=2. The efficiency of E→V energy transfer was determined to be 35%. Our present results were found to be consistent with the impulsive (half-collision) and curve-crossing models.     

Metal-metal and metal-ligand vibrational interaction in compounds of the Fe3EE'(CO)9 (E, E' = S, Se, Te) series and the low-frequency vibrational spectra of Co2FeS(CO)9 and Os3S2(CO)9

The infrared and Raman spectra of the title compounds in the ca. 400-150 cm-1 region are reported. For the first time, detailed assignments are given for all of the features in this region for the first series of compounds. An attempt is made to extend to all of the modes the plastic cluster model of vibrational analysis, which is normally applied only to nu(M-M) vibrations. While mixing occurs between nu(Fe-Fe) and nu(Fe-E), species containing Te posed particular problems; the reasons for this are discussed and give new insights into the plastic cluster model itself.     

Energy dependence of rotational and vibrational distributions of N2(C) for the Ar*(3P0,2) + N2(X) excitation transfer reaction

The Ar* + N₂(X) → N₂(C, v′, N′) + Ar excitation transfer reaction has been investigated experimentally in two different atomic beam experiments. The inelastic cross sections Q_{v′ = 0}(E) and Q_{v′ = 1}(E) to the v′ vibrational level have been measured in the energy range 0.06 ⩽ E(eV) ⩽ 6, using a crossed beam machine. Both cross sections show a behaviour typical for a curve crossing mechanism, with maximum values Q₀ = 8.0 Ų and Q₁ = 1.2 Ų at E = 0.16 eV and E = 0.13 eV, respectively. The oscillatory behaviour of the ratio Q₁(E)/Q₀(E), as first observed by Cutshall and Muschlitz, is also present in our data. Within the model of Gislason et al. the results indicate a decreasing bond stretching with increasing energy. As an alternative we discuss the possibility that the oscillation is due to a different energy dependence of the cross sections for the Ar*(³P₀) and Ar*(³P₂) fine structure states in the mixed beam of metastable Ar*. The vibrational and rotational distributions have also been measured at E = 0.065 eV in a small scale atomic beam-scattering cell experiment, which can be considered as an intermediate between a bulk experiment and a crossed beam experiment. The relative vibrational populations are n_v′ = 100, 16.0, 3.03 and 0.31 for v′ = 0 through 3, with rotational “temperatures” of T_rot,v′ = 1960, 1010, 370 and 130 K. Pronounced deviations (“hump”) of the Boltzmann rotational distributions occur at N′ ≈ 27 for v′ = 0, 1 and 2, with a fractional population of 1, 3 and 11%. For v′ = 0 the “hump” is largely obscured by overlap with the v′ = 1 bandhead. These bimodal distributions are in qualitative agreement with the results of Nguyen and Sadeghi for v′ = 0. The results are discussed within the framework of a curve crossing mechanism with the Ar⁺-N⁻₂ diabatic potential as an intermediate. By assuming equal charges on both N atoms the Coulomb potential of the collinear orientation lies lower (0.45 eV at R = 2.5 Å) than the perpendicular orientation, with the consequence of different transfer probabilities for both orientations. Within a classical model or rotational excitation the final N′ values can be calculated for both orientations, resulting in much higher N′ values for the perpendicular orientation. This mechanism supplies a qualitative explanation for the observed bimodal rotational distributions.     

Reactions of (CO2)2+ and (CO)2+ association ions

The reactons of (CO₂)₂⁺ and (CO)₂⁺ with various additives have been investigated using the NBS high-pressure photoionization mass spectrometer at total pressures of 0.4–1.0 torr of either CO₂ or CO. The additives include CH₄, CD₄, C₂H₂, O₂, H₂O, ^15,14N₂O, and CO in both CO₂ and ¹³CO₂. Second- and third-order rate coefficients based on an ambipolar diffusion model are reported for 25 separate reaction pairs at 295°K, as well as sequential cationic reaction mechanisms. An approximate value of 225 ± 3 kcal/mol (941 ± 13 kJ/mol) was derived for ΔH_f (CO)₂⁺ based on the kinetics observed in various CO-additive mixtures. Some projections regarding the utility of the data under other conditions are also included.     

Intra- and intermolecular vibrational energy transfer in tungsten carbonyl complexes W(CO)5(X) (X=CO, CS, CH3CN, and CD3CN)

Vibrational energy relaxation of degenerate CO stretches of four tungsten carbonyl complexes, W(CO)6, W(CO)5(CS), W(CO)5(CH3CN), and W(CO)5(CD3CN), is observed in nine alkane solutions by subpicosecond time-resolved infrared (IR) pump-probe spectroscopy. Between 0 and 10 ps after the vibrational excitation, the bleaching signal of the ground-state IR absorption band shows anisotropy. Decay of the anisotropic component corresponds either to the rotational diffusion of the molecule or to the intramolecular vibrational energy transfer among the degenerate CO stretch modes. The time constant of the anisotropy decay, tauaniso, shows distinct solvent dependence. By comparing the results for the T1u CO stretch of W(CO)6 and the A1 CO stretch of W(CO)5(CS), the time constant of the rotational diffusion, taur, and the time constant of the intramolecular energy transfer among the three degenerate vibrational modes, taue, are determined as 12 and 8 ps, respectively. The tauaniso value increases as the number of carbon atoms in the alkane solvent increases. After 10 ps, the recovery of the bleaching becomes isotropic. The isotropic decay represents the vibrational population relaxation, from v=1 to v=0. In heptane, the time constant for the isotropic decay, tau1, for W(CO)5(CS) and W(CO)6 was 140 ps. The tau1 for the two acetonitrile-substituted complexes, however, shows a smaller value of 80 ps. The vibrational energy relaxation of W(CO)5(CH3CN) and W(CO)5(CD3CN) is accelerated by the intramolecular energy redistribution from the CO ligand to the acetonitrile ligand. In the nine alkane solutions, the tau1 value of W(CO)6 ranges between 124 and 158 ps, showing the apparent V-shaped solvent dependence with its minimum in decane, while the tau1 value shows little solvent dependence for W(CO)5(CH3CN) and W(CO)5(CD3CN).     

Temperature dependence of the probability of vibrational energy transfer between HF and F

The temperature dependence of the efficiency of vibrational energy transfer in the collinear FH + F and HF + F collisions has been investigated over the temperature range 300°–1500°K by assuming the (8-4) inverse-power potential. The probability P₁₀(T) of vibrational de-excitation (1 → 0) is found to be always very large for FH + F compared to HF + F. At low temperatures P₁₀(T) for FH + F is large; as temperature increases, however, it decreases to a minimum value of ≈8 × 10⁻³ at 900°K, and then slowly increases at higher temperatures. No such unusual temperature dependence is found for HF + F.     

The effects of collision energy, vibrational mode, and vibrational angular momentum on energy transfer and dissociation in NO2+-rare gas collisions: an experimental and trajectory study

A combined experimental and trajectory study of vibrationally state-selected NO2+ collisions with Ne, Ar, Kr, and Xe is presented. Ne, Ar, and Kr are similar in that only dissociation to the excited singlet oxygen channel is observed; however, the appearance energies vary by approximately 4 eV between the three rare gases, and the variation is nonmonotonic in rare gas mass. Xe behaves quite differently, allowing efficient access to the ground triplet state dissociation channel. For all four rare gases there are strong effects of NO2+ vibrational excitation that extend over the entire collision energy range, implying that vibration influences the efficiency of collision to internal energy conversion. Bending excitation is more efficient than stretching; however, bending angular momentum partially counters the enhancement. Direct dynamics trajectories for NO2+ + Kr reproduce both the collision energy and vibrational state effects observed experimentally and reveal that intracomplex charge transfer is critical for the efficient energy transfer needed to drive dissociation. The strong vibrational effects can be rationalized in terms of bending, and to a lesser extent, stretching distortion enhancing transition to the Kr+ -NO2 charge state.     

Theoretical study of Na(4p2P) + Na(3s2S) and Cd(5p3P0) + Na(3s2S) collisions and their role in the energy transfer between Cd.* and Na

We have computed the cross sections for the energy transfer process Cd(5p³P₀) + Na(3s²S) → Cd(5s¹S) + Na(4p²P) and for the state changing collision Na(4p²P) + Na(3s²S) → Na(3d²D) + Na(3s²S), based on theoretical interaction potentials for the NaCd and Na2 systems, respectively. Our calculations shed light on the interpretation of experiments with laser excited Na+Cd vapour mixtures [1]. It turns out that Cd(5p³P₀), in rapid equilibrium with the doorway state Cd(5p³P₁), efficiently transfers energy to Na, populating the 4p²P state. The collisions with ground state Na cause a very fast conversion of the 4p³P₁ to the 3d²D state, from which the strongest emission is observed.     

Distorted wave calculations of vibrational excitation in CO2+He and CO2+Ar collisions

Cross sections for the vibrational excitation and relaxation of CO₂ through collisions with He and Ar atoms have been computed using several approximate methods. They all employ the infinite-order sudden approximation for the rotational motion. The vibrational motion is treated using both exact close-coupling and distorted wave techniques. The latter approximate method permits the extension of the calculation to much higher collision energies. The validity of the distorted wave approximation is examined and is shown to be particularly good for the dominant inelastic processes in He+CO₂, leading to errors of the order of 7%. These become progressively greater for smaller cross sections. The excitation cross sections are reported for several vibrational transitions over an extended energy range up to 1.36 eV.     

Ab initio studies of internal rotation barriers and vibrational frequencies of (C2H2)2, (CO2)2, and C2H2-CO2

We have performed large-scaleab initio calculations using second order Møller-Plesset perturbation theory (MP2) on the three van der Waals dimers formed from acetylene and carbon dioxide. Intermolecular geometrical parameters are reliably computed at this level of theory. Calculations of vibrational frequencies of the van der Waals modes, currently unobtainable by experimental means, give important information about the intermolecular potential and predict significant large-amplitude motion. Zero point energy contributions are shown to be vital in assessing the relative stability of conformations which are close in energy. Our studies suggest that the barrier to interconversion tunnelling in (CO₂)₂ is significantly smaller than previously inferred and is approximately the same as in (C₂H₂)₂. The reason for the rigidity of (CO₂)₂ is the difference in monomer centre-of-mass separation between ground state and transition state. We also show that, in addition to the previously observedC _2v form, the collinear form of C₂H₂-CO₂ is a local minimum on its potential energy surface.     

Calculation of cross sections for penning ionization: He(2S,2S) + H(1S)

Cross sections for ionization of hydrogen atoms by metastable helium atoms are calculated using the best published values for the complex potential. The present cross section for the singlet metastable is quite different from previous determinations. The validity of the JWKB approximation has been verified.     

Pu(7Fg)+CO(X1Σ+,0,0)的分子反应动力学

基于PuCO分子基态()的分析势能函数,用准经典的Monte-Carlo轨线法对Pu(7Fg)+CO(0,0)的分子反应动力学过程进行了计算.结果表明,Pu(7Fg)与CO(0,0)碰撞易生成PuCO络合物分子,该反应是无阈能反应,反应截面σ随能量Et的升高而下降,当Et=502.1kJ@mol-1时,σ几乎为零.     

Resonant vibrational excitation and de-excitation of CO(v) by low energy electrons

Integral cross sections and rate coefficients for vibrational excitation of the excited carbon-monoxide molecule, via the (2)Pi shape resonance in the energy region from 0 to 5 eV have been calculated. Cross sections are calculated by using our recently measured cross sections for the ground level CO excitation and the most recent cross sections for elastic electron scattering, applying the principle of detailed balance. Rate coefficients are calculated for Maxwellian electron energy distribution, with mean electron energies below 5 eV. By using extended Monte Carlo simulations, electron energy distribution functions (EEDF) and rate coefficients are determined in nonequilibrium conditions, in the presence of homogeneous external electric field. Nonequilibrium rates are calculated for typical, moderate values of the electric field over gas number density ratios, E/N, from 1 to 220 Td. Maxwellian and nonequilibrium rate coefficients are compared and the difference is attributed to a specific shape of the electron energy distribution functions under considered conditions.     

State-correlation matrix of the product pair from F + CD(4)--> DF(nu') + CD(3)(0 v(2) 0 0)

The title reaction was investigated under crossed-beam conditions at three different collision energies, E(c) = 8.4, 2.76 and 1.46 kcal mol(-1). The combination of using a (2 + 1) resonance-enhanced multiphoton ionization for tagging state-specific CD(3) products and exploiting a time-sliced velocity imaging for ion detection allows us to reveal the coincident information of the two product pairs in a state-correlated manner. The pair-correlated results are reported for the two product vibrators -- (v(2) = 0, v'), (v(2) = 1, v'), (v(2) = 2, v') and (v(2) = 3, v')-and the dynamics attributes we examined include product state distributions, energy disposals and angular distributions. Together with our earlier communications, a rather complete picture of the correlated dynamics of the title reaction emerges. One of the major findings, the anti-correlated excitations of the two product vibrators at all four energies of this study, can qualitatively be understood by kinematics arguments.