Abstract:, 985 (1994)."Exact" quantum close coupled (CC) and infinite-order sudden approximation (IOSA) calculations have been carried out for the Ar + HF system on an accurate potential energy surface. The differential cross sections from the IOSA calculations show marked differences from the CC results. We find that the energy sudden component of the IOSA breaks down in a different manner for small and large impact parameters, significantly shifting and distorting the state-to-state differential cross sections. We al… Show more
“…Figures −4 show that the minima are N dominated, i.e., the scattering occurs mainly from the repulsive core of the potential. This is consistent with the two-state semiclassical model of refs and , which identifies a minimum in the opacity function and a trajectory deflected by the repulsive part of the potential (but accumulating net zero action), as important for interpreting the minimum in I 1 ← 0 (θ) at E / hc = 1089 cm -1 . 2 Same as Figure except for E / hc = 1089 cm -1 and the transitions (0,0) → (1,0), (0,0) → (1,1).…”
Section: Resultssupporting
confidence: 89%
“…(1) We report accurate quantum coupled-channel (CC) scattering calculations of state-to-state and degeneracy averaged angular distributions using the Hutson potential assuming that HF is a rigid rotator. These calculations, which extend earlier work, ,− have been performed at eight collision energies, with the lowest one being that used in the dopplerimetry experiment of Chapman et al, while the highest one is that employed in the crossed molecular beam experiment of Rawluk et al…”
Section: Introductionmentioning
confidence: 59%
“…There have also been many spectroscopic studies of the ArHF van der Waals complex. Hutson has used the spectroscopic data to construct an intermolecular potential energy function that has performed well in reproducing ,− the scattering measurements (see also refs −13).…”
We report accurate coupled-channel quantum calculations of state-to-state and degeneracy-averaged differential cross sections for the rotationally inelastic collision Ar + HF(V i ) 0, j i ) 0, m i ) 0) f Ar + HF(V f ) 0, j f , m f ), where V i , j i , m i and V f , j f , m f are initial and final vibrational, rotational, and helicity quantum numbers, respectively. The calculations have been performed at eight collision energies and assume that HF is a rigid rotator. Structure in the differential cross sections is analyzed using the unrestricted version of nearsidefarside (NF) theory. The NF theory decomposes the partial wave series (PWS) for the helicity scattering amplitude into two subamplitudes, one N, the other F. This is the first application of NF theory to an atomheteronuclear molecule inelastic collision. It is demonstrated that the NF technique provides a clear physical interpretation of the angular scattering, except sometimes for scattering angles, θ, close to 0°and 180°. It is also shown that a resummation of the PWS can improve the usefulness of the NF technique, when the N and F cross sections possess small oscillations. The resummation procedure exploits recurrence properties of reduced rotation matrix elements to extract a factor (R + βcos θ) -1 from the PWS, where R and β are constants. Criteria for choosing R and β so as to obtain a physically meaningful NF decomposition are discussed.
“…Figures −4 show that the minima are N dominated, i.e., the scattering occurs mainly from the repulsive core of the potential. This is consistent with the two-state semiclassical model of refs and , which identifies a minimum in the opacity function and a trajectory deflected by the repulsive part of the potential (but accumulating net zero action), as important for interpreting the minimum in I 1 ← 0 (θ) at E / hc = 1089 cm -1 . 2 Same as Figure except for E / hc = 1089 cm -1 and the transitions (0,0) → (1,0), (0,0) → (1,1).…”
Section: Resultssupporting
confidence: 89%
“…(1) We report accurate quantum coupled-channel (CC) scattering calculations of state-to-state and degeneracy averaged angular distributions using the Hutson potential assuming that HF is a rigid rotator. These calculations, which extend earlier work, ,− have been performed at eight collision energies, with the lowest one being that used in the dopplerimetry experiment of Chapman et al, while the highest one is that employed in the crossed molecular beam experiment of Rawluk et al…”
Section: Introductionmentioning
confidence: 59%
“…There have also been many spectroscopic studies of the ArHF van der Waals complex. Hutson has used the spectroscopic data to construct an intermolecular potential energy function that has performed well in reproducing ,− the scattering measurements (see also refs −13).…”
We report accurate coupled-channel quantum calculations of state-to-state and degeneracy-averaged differential cross sections for the rotationally inelastic collision Ar + HF(V i ) 0, j i ) 0, m i ) 0) f Ar + HF(V f ) 0, j f , m f ), where V i , j i , m i and V f , j f , m f are initial and final vibrational, rotational, and helicity quantum numbers, respectively. The calculations have been performed at eight collision energies and assume that HF is a rigid rotator. Structure in the differential cross sections is analyzed using the unrestricted version of nearsidefarside (NF) theory. The NF theory decomposes the partial wave series (PWS) for the helicity scattering amplitude into two subamplitudes, one N, the other F. This is the first application of NF theory to an atomheteronuclear molecule inelastic collision. It is demonstrated that the NF technique provides a clear physical interpretation of the angular scattering, except sometimes for scattering angles, θ, close to 0°and 180°. It is also shown that a resummation of the PWS can improve the usefulness of the NF technique, when the N and F cross sections possess small oscillations. The resummation procedure exploits recurrence properties of reduced rotation matrix elements to extract a factor (R + βcos θ) -1 from the PWS, where R and β are constants. Criteria for choosing R and β so as to obtain a physically meaningful NF decomposition are discussed.
“…43 and 54͒ involved systems with low anisotropy of interaction, recent calculations for the collisions of He with CO and the collisions of Ar and He with OH 55-57 -systems possessing high anisotropy of interaction-showed a good agreement of the CS results with both more accurate coupled channel calculations and experimental data where available. In the case of ArϩHF collisions the CS approximation was investigated by Barrett and co-workers 58 who performed a semiclassical study of rotationally inelastic scattering on the H6 PES 37 which is similar to the PES we use in the present work. The authors 58 found that the CSA results agreed very well with their full semiclassical calculations.…”
Section: Resultsmentioning
confidence: 99%
“…In the case of ArϩHF collisions the CS approximation was investigated by Barrett and co-workers 58 who performed a semiclassical study of rotationally inelastic scattering on the H6 PES 37 which is similar to the PES we use in the present work. The authors 58 found that the CSA results agreed very well with their full semiclassical calculations. To evaluate the error of the CSA in the present work we also perform full close coupling calculations of cross sections for multiple quantum rotational transitions in the HF(vϭ0, jϭ0)ϩAr collisions.…”
Vibrational relaxation cross sections and rate constants of HF(vϭ1) by Ar are calculated on a recent semiempirical potential energy surface ͑PES͒ ͓J. Chem. Phys. 111, 2470 ͑1999͔͒ using the quantum-mechanical coupled states approach. Accurate theoretical estimations of rate coefficients for vibrational relaxation of HF(vϭ1) at temperatures between 100 and 350 K are obtained. The vibrational relaxation is shown to be of a quasiresonant character and occur mostly to two nearest rotational levels of the ground vibrational state. The weak isotope effect after substitution of HF by DF is investigated and explained. The cross sections for vibrational relaxation of HF(v, jϭ0), where vϭ1,2,3,4, are calculated and shown to increase significantly as v increases. In the same calculations we observe a dramatic increase of multiple quantum vibrational transitions as the difference between the initial and final states falls in close resonance with the collision energy. A comparison of the cross sections obtained from the coupled states calculations with those performed with rotational infinite-order-sudden approximation proves a crucial role of molecular rotations for vibrational relaxation. Finally, we describe the close coupling coupled states calculations for relaxation and rotational excitation of HF(vϭ1, jϭ0) with a reduced number of open channels in the basis set and show that it is possible to obtain converged results for rotationally inelastic transitions between the various levels of vϭ1 neglecting all states below vϭ1, jϭ0.
In a previous article [A. J. H. M. Meijer, G. C. Groenenboom, and A. van der Avoird, J. Chem. Phys. 101, 7603 (1994)] we investigated the energy dependence of the steric effect of the reaction Ca ( *D)+CH3F (jkm = 111) ->CaF (A 2ri)+ C H 3 using a quasiclassical trajectory method. It was found that we could not reproduce the experimental results for this reaction [M. H. M. Janssen, D. H. Parker, and S. Stolte, J. Phys. Chem. 95, 8142 (1991)]. In this article, we reinvestigate this reaction using a semiclassical method, in which the rotation of the molecule and the electronic states of the interacting atom and molecule are treated quantum mechanically. For the chemical reaction we use a model which correlates the projection of the electronic orbital angular momentum of the Ca atom on the intermolecular axis with the projection of the electronic orbital angular momentum of the CaF product on the diatomic axis [M. Menzinger, Polon. Phys. Acta A 73, 85 (1988)]. This model is applied to examine the CaF (A 2U , B 22 + , A' 2A) exit channels separately. We conclude that we can reproduce the experimental results for the steric effect using this model. The improvement with respect to the classical trajectory results is shown to be due primarily to the extended reaction model rather than to the semiclassical description of the dynamics. We find trapping and reorientation in the semiclassical calculations, as in the previous classical trajectory results, but also non-adiabatic effects are present. The latter do not affect the reactive cross sections very much.
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