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Collisional and photoinitiated reaction dynamics in the ground electronic state of Ca–HCl

AuthorsSanz, Cristina; Avoird, Ad van der; Roncero, Octavio
Chemical exchanges
Hydrogen compounds
Atom-molecule reactions
Ground states
Rotational-vibrational states
Potential energy surfaces
Infrared spectra
Excited states
Binding energy
Bond lengths
Wave functions
Reaction kinetics theory
Charge exchange
[PACS] Atom and radical chemical reactions; chain reactions, molecule-molecule reactions
[PACS] Photochemistry
[PACS] Potential energy surfaces for chemical reactions
[PACS] Ion–molecule, ion–ion, and charge-transfer chemical reactions
[PACS] State to state energy transfer in chemical reactions
[PACS] Collision theories and trajectory models of chemical kinetics
[PACS] Infrared molecular spectra
[PACS] Molecular ionization potentials, electron affinities, molecular core binding energy
[PACS] Interatomic distances and angles in molecules
Issue Date12-Aug-2005
PublisherAmerican Institute of Physics
CitationJournal of Chemical Physics 123(6): 064301 (2005)
AbstractCa+HCl(ν,j) reactive collisions were studied for different rovibrational states of the HCl reactant using wave-packet calculations in reactant Jacobi coordinates. A recently proposed potential-energy surface was used with a barrier of ≈ 0.4 eV followed by a deep well. The possibility of an insertion mechanism due to this last well has been analyzed and it was found that once the wave packet passes over the barrier most of it goes directly to CaCl+H products, which shows that the reaction dynamics is essentially direct. It was also found that there is no significant change in the reaction efficiency as a function of the initial HCl rovibrational state, because CaHCl at the barrier has an only little elongated HCl bond. Near the threshold for reaction with HCl(ν=0), however, the reaction shows significant steric effects for j>0. In a complementary study, the infrared excitation from the Ca–HCl van der Waals well was simulated. The spectrum thus obtained shows several series of resonances which correspond to quasibound states correlating to excited HCl(ν) vibrations. The Ca–HCl binding energies of these quasibound states increase dramatically with ν, from 75 to 650 cm–1, because the wave function spreads increasingly over larger HCl bond lengths. Thus it explores the region of the barrier saddle point and the deep insertion well. Although also the charge-transfer contribution increases with ν, the reaction probability for resonances of the ν=2 manifold, which are well above the reaction threshold, is still negligible. This explains the relatively long lifetimes of these ν=2 resonances. The reaction probability becomes significant at ν=3. Our simulations have shown that an experimental study of this type will allow a gradual spectroscopic probing of the barrier for the reaction.
Description11 pages, 14 figures, 1 table.-- PACS nrs.: 82.30.Cf; 82.50.-m; 82.20.Kh; 82.30.Fi; 82.20.Rp; 82.20.Fd; 33.20.Ea; 33.15.Ry; 33.15.Dj; 82.30.Hk.
Publisher version (URL)http://dx.doi.org/10.1063/1.1995700
Appears in Collections:(CFMAC-IFF) Artículos
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