ISSN:
0020-7608
Keywords:
Computational Chemistry and Molecular Modeling
;
Atomic, Molecular and Optical Physics
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The interaction of the CO2 molecule with a single palladium atom has been studied by means of a linear combination of Gaussian type orbitals-density functional (LCGTO-DF) method, as implemented in the code deMon. Local and nonlocal functionals were used. The core electrons of the palladium atom were represented by a model core potential, which includes relativistic effects. Several coordination modes of the CO2 moiety to the Pd atom were studied. They were fully optimized by allowing both electronic and structural relaxation. The calculations indicate a dihapto CO (η2-CO) coordination mode (or mixed Pd—C/Pd—O bonding), of Cs symmetry, as the one of lowest energy. There is a strong charge transfer from Pd to CO2, which produces a large structural change in CO2: It goes from a linear to a bent geometry. The calculated frequencies of CO2 in Pd—CO2 are 689, 1212, and 2018 cm-1 for the bending, symmetric, and asymmetric vibrational modes, respectively. These results agree reasonably with the observed frequencies of CO2 adsorbed on H2O/Pd(110) and Pd(111)/Na surfaces. The η2-CO structure is a likely candidate for the adsorption of CO2 on palladium surfaces, since the asymmetric mode is observed. This mode is dipole allowed in Cs symmetry but dipole forbidden in C2v. The monohapto C (η1-C) coordination mode, of C2v symmetry, was found to be a transition state, 2.2 and 8.4 kcal/mol, for the local and nonlocal levels, respectively, above the (η2-CO) minimum. The η2-O—O mode is not attainable for Pd—CO2; calculations started with this configuration converge to the η2-CO mode, the ground state. This is a quite different picture to that found for Ni—CO2, where the moiety is chemisorbed in the dihapto η2-O—O coordination mode. © 1994 John Wiley & Sons, Inc.
Additional Material:
3 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/qua.560520857
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