Hydrogen interactions with a Pd₄ cluster: Triplet and singlet states and transition probability

TY - JOUR

T1 - Hydrogen interactions with a Pd4 cluster

T2 - Triplet and singlet states and transition probability

AU - German, Ernst D.

AU - Efremenko, Irena

AU - Sheintuch, Moshe

PY - 2001/12/20

Y1 - 2001/12/20

N2 - The DFT method is used to analyze the singlet and triplet PES cross-sections for a number of reaction pathways of the interaction between a hydrogen molecule and a palladium tetramer. Stationary points characterizing stable singlet and triplet complexes and transition states are determined. Predissociated Pd4H2 complexes with binding energies of 5.0-6.4 kcal/mol are formed without an activation barrier at any initial orientation of reactants in the ground triplet state. The dissociated triplet complexes with adsorption energy of 4.7-8.4 kcal/mol are separated from the predissociated structures by the barrier of 11 kcal/mol. The dissociated singlet structures with hydrogen atoms located in two 3-fold positions and in the bridge positions on nonintersecting Pd-Pd bonds have the same binding energy of 22.1 kcal/mol and correspond to the ground state of the Pd4H2 system. Several more local minima corresponding to dissociated and nondissociated H-H bonds are found on the singlet PES. In contrast to the low-index bulk palladium surfaces, no spontaneous pathway for hydrogen dissociation on the cluster is found. Activated H2 dissociation on the palladium tetramer includes the triplet-singlet transition induced by the spin-orbit interaction as a key step. Numerical estimation of the matrix spin-orbit coupling element and the corresponding transmission coefficient κ is performed within nonadiabatic theory for two reaction pathways, which are expected to have the maximal reaction probability. The estimated κ values of ∼0.1 and ∼0.4 and corresponding activation barriers of ∼25 and ∼20 kcal/mol are found for the reaction pathways leading to the ground-state three-coordinated dissociated complex and to the saddle point heading toward the ground-state bridge structure, respectively.

AB - The DFT method is used to analyze the singlet and triplet PES cross-sections for a number of reaction pathways of the interaction between a hydrogen molecule and a palladium tetramer. Stationary points characterizing stable singlet and triplet complexes and transition states are determined. Predissociated Pd4H2 complexes with binding energies of 5.0-6.4 kcal/mol are formed without an activation barrier at any initial orientation of reactants in the ground triplet state. The dissociated triplet complexes with adsorption energy of 4.7-8.4 kcal/mol are separated from the predissociated structures by the barrier of 11 kcal/mol. The dissociated singlet structures with hydrogen atoms located in two 3-fold positions and in the bridge positions on nonintersecting Pd-Pd bonds have the same binding energy of 22.1 kcal/mol and correspond to the ground state of the Pd4H2 system. Several more local minima corresponding to dissociated and nondissociated H-H bonds are found on the singlet PES. In contrast to the low-index bulk palladium surfaces, no spontaneous pathway for hydrogen dissociation on the cluster is found. Activated H2 dissociation on the palladium tetramer includes the triplet-singlet transition induced by the spin-orbit interaction as a key step. Numerical estimation of the matrix spin-orbit coupling element and the corresponding transmission coefficient κ is performed within nonadiabatic theory for two reaction pathways, which are expected to have the maximal reaction probability. The estimated κ values of ∼0.1 and ∼0.4 and corresponding activation barriers of ∼25 and ∼20 kcal/mol are found for the reaction pathways leading to the ground-state three-coordinated dissociated complex and to the saddle point heading toward the ground-state bridge structure, respectively.

UR - http://www.scopus.com/inward/record.url?scp=0035924875&partnerID=8YFLogxK

U2 - 10.1021/jp012796+

DO - 10.1021/jp012796+

M3 - 文章

AN - SCOPUS:0035924875

SN - 1089-5639

VL - 105

SP - 11312

EP - 11326

JO - Journal of Physical Chemistry A

JF - Journal of Physical Chemistry A

IS - 50

ER -