Volume 124, 2003

Modelling spin-forbidden reactions: recombination of carbon monoxide with iron tetracarbonyl

Abstract

New density functional theory and ab initio computations on the [Fe(CO)5] system are reported. Careful exploration of basis set and correlation effects leads to “best” values for the difference in energy ΔE(1,3) between ground state 3[Fe(CO)4] and the singlet excited state of ca. 8 kcal mol−1, and for the bond dissociation energy BDE(3) of [Fe(CO)5] with respect to ground state fragments 3[Fe(CO)4] + CO of ca. 40 kcal mol−1. A modified form of the B3PW91 functional is used to explore the potential energy surface for the spin-forbidden recombination reaction of CO with 3[Fe(CO)4]. A Cs-symmetric minimum energy crossing point (MECP) between the reactant (triplet) and product (singlet) potential energy surfaces is found, lying 0.43 kcal mol−1 above the reactants. The rate coefficient for recombination is computed using a non-adiabatic form of transition state theory, in which the MECP is treated as the critical point in the reaction. Semi-quantitative agreement with experiment is obtained: the predicted rate coefficient, 8.8 × 10−15 cm3 molecule−1 s−1, is only six times smaller than the experimental rate. This is the first computation from first principles of a rate coefficient for a spin-forbidden reaction of a transition metal compound.

Article information

Article type
Paper
Submitted
28 Nov 2002
Accepted
29 Nov 2002
First published
25 Apr 2003

Faraday Discuss., 2003,124, 129-143

Modelling spin-forbidden reactions: recombination of carbon monoxide with iron tetracarbonyl

J. N. Harvey and M. Aschi, Faraday Discuss., 2003, 124, 129 DOI: 10.1039/B211871H

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