Laser-induced fluorescence study of reactions of Ba with HCl and HBr at different collision energies

Siegel, A.; Schultz, A.

doi:10.1063/1.439081

Cited by 43 publications

(10 citation statements)

References 17 publications

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“…In some reactions of this family, as in the CaϩHF reaction, the insertion pathway has been shown to be dominant, 2 whereas in others, such as the Ba ϩHBr and BaϩHCl reactions, the reactions appear to proceed through a direct abstraction pathway. 3,4 The MϩHX reaction family is also characterized by a special mass combination, namely, that of ''heavy atom ϩheavy-light diatomic molecule.'' The large difference be-tween reactant and product reduced masses largely dictates the fate of the reactant angular momentum.…”

Section: Introductionmentioning

confidence: 99%

Energy and angular momentum control of the specific opacity functions in the Ba+HI→BaI+H reaction

Kalogerakis

Zare

1996

The Journal of Chemical Physics

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Vibration-rotation excitation of CO by hot hydrogen atoms: Comparison of two potential energy surfacesCrossed-beam and beam-gas experiments on the reaction BaϩHI→BaIϩH have been performed, in which the most probable collision energy ranges from 3 to 17 kcal/mol. The results, combined with previous experimental studies on this reaction system, show a remarkable collision energy dependence. Between low and high collision energies, a transition occurs in the intensity, width, and peak location of the product vibrational and rotational population distributions. The onset of this transition is estimated to occur at approximately 5 kcal/mol. For collision energies smaller than 5 kcal/mol, the product vibrational distribution is bell shaped and peaks at vϭ12. For collision energies larger than 5 kcal/mol, a second maximum appears at vϭ0 in the vibrational distribution. The rotational distributions of the crossed-beam experiments are extremely narrow but broaden at lower collision energies. As the collision energy is increased above 5 kcal/mol, the BaI rotational excitation is very near the energetic limit, and the maximum for the BaI͑vϭ0͒ rotational population distribution moves from Jϭ415.5 to Jϭ538.5. In contrast, below the transition onset, the maximum remains unchanged around Jϭ420.5. Moreover, the peaks of the BaI͑vϭ1͒ and BaI͑vϭ2͒ rotational distributions appear at successively lower J values, as expected from energy conservation arguments. The nature of the kinematic constraints for this reaction allows the determination of the opacity functions for the production of the BaI product in a specific vibrational level v. Detailed analysis of the collision energy dependence of the specific opacity functions offers insight into the role of conservation of energy and angular momentum in influencing this reaction. At low collision energies, the maximum reactive impact parameter, b max , is determined by an angular momentum ͑centrifugal͒ barrier. At collision energies larger than 5 kcal/mol, conservation of energy dictates the value of b max . These two processes are identified as the mechanisms that control the BaϩHI reaction cross section. The transition between the two mechanisms provides an interpretation for the bimodal character of the BaI product internal-state distribution.

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Section: Introductionmentioning

confidence: 99%

Energy and angular momentum control of the specific opacity functions in the Ba+HI→BaI+H reaction

Kalogerakis

Zare

1996

The Journal of Chemical Physics

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“…Indeed the study of these types of reaction constitutes one of the best examples where important kinematic factors control the scalar and vector properties of elementary chemical reactions. Among this class of reaction, the family of heavy atom plus HX (where X = halogen) processes has been studied extensively [10][11][12][13][14][15][16][17][18][19][20]. From the scalar point of view it is well known that useful information about the reaction cross-section, including its collision energy dependence, can be gained by measuring the rotational energy distribution of the product [21 , 22].…”

Section: Introductionmentioning

confidence: 99%

Angular momenta correlation in kinematically constrained reactions: application to the Ba + HI → BaI + H system

et al. 1995

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Extensive quasiclassical trajectory calculations have been carried out to study the disposal of both rotational and orbital angular momenta in the Ba + HI ~ BaI + H system. As expected for this kinematically constrained reaction, a complete transfer of the reactant orbital (rotational) momentum L(J) into the product rotational (orbital) angular momentum J'(L') was found. However, significant deviations from the kinematic limit are noticeable for the J ~ L' vector correlation, particularly at low reagent rotational excitation. The results are analysed in the light of the stereodynamic picture associated with these kinematically restricted reactions. In addition, the possibility of controlling the spatial distribution of the reaction products by laser polarization of the reagent rotational angular momentum is also discussed.

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“…Specific reactions investigated experimentally under single collision conditions include: Ca + HF,I,3 Ca + HI, 2 Sr + HF,3-8 Sr + HI, 2 Ba + HF,6,8-12 Ba + HCI,9.13.14 Ba + HBr,9,14 and Ba + HI. 2 ,9,I5 Despite the rather substantial data base provided by these experimental studies, no fully comprehensive theoretical and/or intuitive understanding of the microscopic dynamical features of this class of reactions has emerged.…”

Section: Introductionmentioning

confidence: 99%

Ca+HF: The anatomy of a chemical insertion reaction

Jaffe

Pattengill

Mascarello

et al. 1987

The Journal of Chemical Physics

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A comprehensive first principles theoretical investigation of the gas phase reaction Ca + HF -CaF + H is reported. The overall study involves three distinct elements: (a) generation of an accurate ab initio potential energy surface for the ground electronic state of the Ca-F-H system, (b) careful fitting of the computed surface to an analytical form suitable for three-dimensional reactive scattering calculations, and (c) execution of classical trajectory calculations for Ca + HF collisions using the fitted potential surface. Ab initio potential energy calculations were performed for 175 Ca-F-H geometries using an MCSCF-CI method with a large Gaussian orbital basis set. The error in the computed endothermicity for the reaction of Ca and HF is less than I kcallmol and the errors in the computed saddle point energies are believed to be less than 3 kcallmol. The potential energy surface is dominated by a deep well corresponding to a stable linear H-Ca-F intermediate with an extremely small bending force constant. The calculations clearly demonstrate that the preferred geometry for Ca attack on HF is markedly noncollinear. The saddle point for both fluorine exchange reaction and insertion into the H-Ca-F well occurs for a Ca-F-H angle of 75° and has an energy of 16.1 kcallmol relative to Ca + HF. The energy barrier for collinear reaction, 30.0 kcallmol, is nearly twice as high. The analytical representation of the ab initio potential energy surface is based on a polynomial expansion in the three diatomic bond lengths that reproduces the values of the computed energies to within a root mean square deviation of 1.2 kcallmol and reduces to the appropriate diatomic potentials in the asymptotic limits. Classical trajectory calculations for Ca + HF(v = 1) utilizing the fitted surface establish the fact that the H-Ca-F potential well dominates the collision dynamics thus qualifying Ca + HF as a bona fide example of a chemical insertion reaction. Because of the extensive sampling of the H-Ca-F well, many trajectories formed rather long-lived intermediate complexes before reaching diatomic end products. A significant number of these trajectories were not converged with respect to changes in the integration time step. Despite uncertainties associated with the ultimate fates of the nonconverged trajectories, the results obtained support a number of generalizations relating to microscopic features of Ca + HF collisions. Among these are: (1) at fixed total collision energy, excitation of HF to v = I is much more effective in promoting reaction than is placing the corresponding amount of energy in Ca,HF translation, (2) at fixed initial translational energy, reaction cross sections increase with increasing HF rotational quantum number J, (3) for trajectories which enter the H-Ca-F well, escape to form products is favored by increasing initial HF rotation and escape back to reactants is favored by increasing the initial relative translational energy, and (4) the CaF fractional product energy disposals are remarkably independent of i...

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Laser-induced fluorescence study of reactions of Ba with HCl and HBr at different collision energies

Cited by 43 publications

References 17 publications

Energy and angular momentum control of the specific opacity functions in the Ba+HI→BaI+H reaction

Energy and angular momentum control of the specific opacity functions in the Ba+HI→BaI+H reaction

Angular momenta correlation in kinematically constrained reactions: application to the Ba + HI → BaI + H system

Ca+HF: The anatomy of a chemical insertion reaction

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