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| 2. |
- Andersson, Stefan, 1973, et al.
(author)
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Computational studies of the kinetics of the C+NO and O+CN reactions
- 2003
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In: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 107:28, s. 5439-5447
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Journal article (peer-reviewed)abstract
- Thermal rate coefficients for the reactions C(3P) + NO(X2Π) → CN(X2Σ+) + O(3P), C(3P) + NO(X2Π) → CO(X1Σ+) + N(2D), and O(3P) + CN(X2Σ+) → CO(X1Σ+) + N(2D) in the temperature range from 5 to 5000 K have been obtained using quasiclassical trajectory calculations. Results are reported for two ab initio potential energy surfaces corresponding to states of 2A‘ and 2A‘ ‘ symmetry. Good agreement between calculated and experimental rate coefficients are obtained for the C + NO reactions for all temperatures, whereas the rate coefficient for the O + CN reaction at room temperature is larger than that found experimentally. The dynamics is considerably different on the two potential energy surfaces with the 2A‘ ‘ giving rate coefficients in better agreement with experiments. The quality of the potential energy surfaces are discussed in the light of new electronic structure calculations including spin−orbit coupling.
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| 3. |
- Barinovs, G, et al.
(author)
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Propagation of 3D wave packets for nonzero total angular momentum using the split operator method
- 2001
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In: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 105:31, s. 7441-7445
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Journal article (peer-reviewed)abstract
- Three-dimensional wave packet calculations for total angular momentum quantum number J ≥ 0 have been performed in Jacobi coordinates. To be able to use the split operator propagator together with the fast Fourier transform method, the wave function is transformed and a modified Hamiltonian obtained. The filter diagonalization method has been used to determine a few rovibrational eigenstates of the H2O molecule on the lowest potential energy surface. Good agreement with previous work is obtained.
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| 4. |
- Bäck, A, et al.
(author)
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Investigation of quantum effects on vibrational excitation of CF3Br scattering from graphite
- 2002
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In: Chemical Physics. - 0301-0104. ; 285:2-3, s. 233-244
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Journal article (peer-reviewed)abstract
- Mixed quantum–classical molecular dynamics simulations of vibrational excitation of CF3Br in collisions with graphite have been carried out. The quantum problem is made numerically manageable by a reduced dimensionality treatment of the internal degrees of freedom including only the C–Br stretch and the umbrella motion. These two coordinates are treated quantum mechanically as a 2D wavepacket whereas the translational and rotational degrees of freedom and the surface atoms are treated classically. A 3D wavepacket scheme where the distance to the surface is included among the quantum degrees of freedom is also considered as well as purely classical trajectories. It is found that the total vibrational excitation is quite low. Excitation of the C–Br stretch dominates with only a very small fraction of the excitation energy going into the umbrella motion. The 2D wavepacket calculations and the classical trajectories (initiated without zero point energy) give nearly identical results for the total excitation but the 2D wavepacket model excites the umbrella motion to a lesser extent. The 3D wavepacket method shows a considerable dependence on the initial width of the wavepacket due to the underlying mean-field approximation. All methods show a linear increase in vibrational excitation with increasing surface temperature, in agreement with previous experimental results.
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| 5. |
- Krems, RV, et al.
(author)
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Resonance and reversibility of vibrational relaxation of HF in high temperature Ar bath gas
- 2002
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In: Journal of Chemical Physics. - 1089-7690 .- 0021-9606. ; 117:1, s. 166-171
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Journal article (peer-reviewed)abstract
- The Boltzmann averaged rate constants for total vibrational relaxation of HF(v = 1) in collisions with Ar are computed in the range of temperatures between 100 and 1500 K. The computed rate constants overestimate the experimental measurements at high temperatures by a large factor. It is concluded that the deviation between theory and experiment cannot be explained by inaccuracy of the PES or dynamical approximations made. It is shown that increasing initial rotational energy enhances a resonant character of the vibrational energy transfer to a great extent. An assumption is made that total vibrational relaxation of HF(v = 1) at high temperatures is determined by competition between vibrational relaxation to a resonant level (v = 0,jres), vibrational excitation from the resonant level, and purely rotational relaxation of HF(v = 0,jres). It is demonstrated that at high temperatures the latter process can be significantly slower than vibrationally inelastic transitions and rotational relaxation of HF(v = 0,jres) may in fact be a rate-limiting stage of vibrational relaxation.
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| 6. |
- Markovic, Nikola, 1961, et al.
(author)
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Mixed quantum-classical scattering dynamics of CF3Br
- 2004
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In: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 108:41, s. 8765-8771
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Journal article (peer-reviewed)abstract
- The vibrational excitation of CF3Br scattering from graphite has been studied using mixed quantum−classical methods. A previously investigated 2D model for the intramolecular degrees of freedom [Bäck, A.; Marković, N. Chem. Phys. 2002, 285, 233] has been extended to 3D including all vibrations of a1 symmetry, improving the dynamical description of the umbrella mode. We investigate the details of the excitation process for a few selected initial conditions as well as the general effect of surface temperature for ensembles of randomly sampled trajectories. Quantum results are obtained from 3D wave packet propagations and calculations based on the time-dependent Gauss−Hermite discrete variable representation method. When the quantum data are compared with classical results it is confirmed that quantization of the internal degrees of freedom does indeed have a very small effect for the present system. Considering vibrational excitation from the ground state, almost perfect agreement between quantum and classical calculations is found, provided that the classical trajectories are initialized without vibrational energy.
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| 7. |
- Tomsic, A, et al.
(author)
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Collision dynamics of large water clusters on graphite
- 2003
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In: Journal of Chemical Physics. - 1089-7690 .- 0021-9606. ; 119:9, s. 4916-4922
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Journal article (peer-reviewed)abstract
- The emission of neutral cluster fragments during collisions of large water clusters with graphite surfaces has been investigated using molecular beam techniques. Water clusters with an average size of up to 1.4·104 molecules per cluster collide with the surface with a velocity of 1380 ms–1. Angular distributions for emitted large fragments are shifted towards the tangential direction and become increasingly narrow with increasing fragment size. The kinetic energy in the surface normal direction is efficiently transferred to internal degrees of freedom and to surface modes, while the momentum parallel to the surface plane is less affected by the surface interaction. Both a direct scattering channel and an emission channel mediated by cluster evaporation are concluded to be of importance for the collision outcome. The results for the evaporation-mediated emission channel agree well with previous experimental investigations and with recent molecular dynamics simulations, and the observations regarding the direct scattering channel qualitatively agree with the dynamics observed for macroscopic particles colliding with surfaces.
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| 8. |
- Tomsic, A, et al.
(author)
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Molecular-dynamics simulations of cluster-surface collisions: Emission of large fragments
- 2001
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In: Journal of Chemical Physics. - : AIP Publishing. - 1089-7690 .- 0021-9606. ; 115:22, s. 10509-10517
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Journal article (peer-reviewed)abstract
- Large-scale classical molecular-dynamics simulations of (H2O)n (n = 1032,4094) collisions with graphite have been carried out. The clusters have an initial internal temperature of 180 K and collide with an incident velocity in the normal direction between 200 and 1000 m/s. The 1032-clusters are trapped on the surface and completely disintegrate by evaporation. The 4094-clusters are found to partly survive the surface impact provided that the surface is sufficiently hot. These clusters are trapped on the surface for up to 50 ps before leaving the surface under strong evaporation of small fragments. The time spent on the surface is too short for full equilibration to occur, which limits the fragmentation of the clusters. The size of the emitted fragment is roughly 30% of the incident cluster size. The cluster emission mechanism is found to be very sensitive to the rate of the surface-induced heating and thus to the surface temperature. The incident cluster velocity is less critical for the outcome of the collision process but influences the time spent on the surface. The trends seen in the simulations agree well with recent experimental data for collisions of large water clusters with graphite [Chem. Phys. Lett. 329, 200 (2000)].
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| 9. |
- Tomsic, A, et al.
(author)
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Molecular dynamics simulations of cluster-surface collisions: Mechanisms for monomer emission
- 2001
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In: Physical Chemistry Chemical Physics. - 1463-9084 .- 1463-9076. ; 3:17, s. 3667-3671
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Journal article (peer-reviewed)abstract
- Molecular dynamics simulations of (H2O)4094-clusters impacting with a velocity of 470 ms–1 in the normal direction on a graphite surface kept at 1400 K were performed. The aim was to clarify the behavior of water molecules and other small fragments emitted during the collision event. The results agree well with previous experimental studies and with the results of a thermokinetic model for evaporation of small fragments during cluster scattering. About 80% of the evaporating water molecules come in close contact with the hot surface, and their translational degrees of freedom are partly accommodated to the temperature of the surface, especially in the direction normal to the surface plane, leading to a high translational temperature in this direction. The results stress the importance of energy transfer from the hot surface to the cluster and explain the high translational temperature determined from experimental angular distributions.
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| 10. |
- Tomsic, A, et al.
(author)
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Scattering of Ice particles from a graphite surface: A molecular dynamics simulation study
- 2003
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In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 107:38, s. 10576-10582
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Journal article (peer-reviewed)abstract
- Large-scale classical trajectory calculations of (H2O)n, n ≤ 25 159, colliding with a graphite surface have been carried out in order to relate the phenomenon of direct scattering to the initial conditions of the collision. The collisions were performed at normal incidence with the incident velocity ranging from 50 to 2000 ms-1 and at surface temperatures between 300 and 1400 K. Upon impact, the cluster is deformed elastically (reversibly) and plastically (irreversibly), and if the elastically stored energy is larger than the binding energy between the cluster and the surface, the cluster scatters directly from the surface. The partitioning between elastic and plastic deformation is governed by the initial conditions (cluster temperature, incident velocity, incident cluster size, and surface temperature). At low incident velocities the scattering probability is controlled by adhesion and at high incident velocities by plastic deformation, and the direct scattering is thus confined to a narrow range of incident velocities. The results are in qualitative agreement with recent experimental studies of water clusters scattering from graphite.
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