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Issue 30, 2011
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Quantum stereodynamics of Li + HF reactive collisions: the role of reactants polarization on the differential cross section

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Abstract

A complete quantum study for the state-to-state Li + HF(v,j,m) → LiF(v′,j′,Ω′) + H reactive collisions has been performed using a wave packet method, for different initial rotational states and helicity states of the reactants. The state-to-state differential cross section has been simulated, and the polarization of products extracted. It is found that the reactivity is enhanced for nearly collinear collisions, which produces a vibrational excitation of HF, needed to overcome the late barrier. It is also found that LiF(v′ = 0) products are preferentially forward scattered, while vibrationally excited LiF(v′ = 1 and 2) are backward scattered. These results are interpreted with a simple reaction mechanism, based on the late character and bent geometry of the transition state, originating from a covalent/ionic crossing, which consists of two steps: the arrival at the transition state and the dissociation. In the first step, in order to get to the saddle point some HF vibrational excitation is required, which favors head-on collisions and therefore low values of m. In the second step a fast dissociation of H atom takes place, which is explained by the ionic Li+FH character of the bent transition state: the FH is repulsive making that H depart rapidly leaving a highly rotating LiF molecule. For the higher energy analyzed, where resonances slightly contribute, the orientation and alignment of product rotational states, referred to as reactants frame (with the z-axis parallel to k), are approximately constant with the scattering angle. The alignment is close to −1, showing that j′ is perpendicular to k, while starting from initial states with well defined rotational orientation, as states with pure m values, the final rotational are also oriented. It is also found that when using products frame (with the z′-axis parallel to k′) the rotational alignment and orientation of products varies a lot with the scattering angle just because the z′ axis changes from being parallel to anti-parallel to k when varying from θ = 0 to π.

Graphical abstract: Quantum stereodynamics of Li + HF reactive collisions: the role of reactants polarization on the differential cross section

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Publication details

The article was received on 08 Nov 2010, accepted on 09 May 2011 and first published on 04 Jul 2011


Article type: Paper
DOI: 10.1039/C0CP02452J
Citation: Phys. Chem. Chem. Phys., 2011,13, 13656-13669
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    Quantum stereodynamics of Li + HF reactive collisions: the role of reactants polarization on the differential cross section

    L. González-Sánchez, O. Vasyutinskii, A. Zanchet, C. Sanz-Sanz and O. Roncero, Phys. Chem. Chem. Phys., 2011, 13, 13656
    DOI: 10.1039/C0CP02452J

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