Femtochemistry of bimolecular reactions from weakly bound complexes: computational study of the H + H ′ OD − −− → H ′ OH + D/HOD + H ′ exchange reactions
Résumé
A full-dimensional wavepacket propagation describing the bimolecular exchange reactions H +H′OD −−→H′OH + D / HOD + H′ initiated by photolysis of HCl in the hydrogen-b ound complex(HCl) ···(HOD) is rep orted. The dynamics of this reaction is carried out with the MCTDH metho don an ab initio p otential energy surface (PES) of H3 O and the initial state is derived from the groundstate wavefunction of the complex obtained by relaxation on its own electronic ground state ab initioPES. The description of the system makes use of p olyspherical co ordinates parametrizing a set ofRadau and Jacobi vectors. The calculated energy- and time-resolved reaction probabilities show,owing to the large collision energies at play stemming from the (almost full) photolysis of HCl, thatthe repulsion b etween oxygen in the H′OD molecule and the incoming hydrogen atom is the mainfeature of the collision and leads to non-reactive scattering. No abstraction reaction pro ducts areobserved. However, b oth exchange pro cesses are still observable, with a preference in O H′ b onddisso ciation over that of O D. The selectivity is reversed up on vibrational pre-excitation of the O Dstretching mo de in the H′OD molecule. It is shown that, after the collision, the hydrogen atom ofHCl do es most likely not encounter the almost stationary chlorine atom again but we also considerthe limit case where the H atom is forced to collide multiple times against H′OD as a result of b eingpushed back by the Cl atom.
Domaines
Chimie théorique et/ou physique
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