The gas-phase equilibria NO;.(HONO), \_, + HONO# NO?(HONO), were measured in a high-prrssurc mass spcctromc-1cr between 240 and 350 I(. The following enthalpy channgcs were detcrmined:A.H:,1 = -31. aHy.2 = -21.6 and A$ 3 = -20.3 kcal/mol. These results are discussed in rchtion to the structures of N
Interaction of NO molecules with Pd clusters: Ab initio density–functional study
✍ Scribed by Robert Grybos; Lubomir Benco; Tomas Bučko; Jürgen Hafner
- Publisher
- John Wiley and Sons
- Year
- 2009
- Tongue
- English
- Weight
- 573 KB
- Volume
- 30
- Category
- Article
- ISSN
- 0192-8651
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✦ Synopsis
Abstract
The adsorption of NO molecules on small Pd~n~ (n = 1−6) clusters has been studied using first‐principles density‐functional theory. Three adsorption sites were considered: vertex (on–top), bridge, and hollow. Adsorption is strong, ranging from 2 to 3 eV. In all cases NO adsorbs in a bent configuration. Calculated shifts in N–O bond vibration frequencies (with anharmonic corrections) agree very well with available experimental data. In contrast to metallic Pd surfaces, adsorption of NO on palladium clusters causes considerable changes in geometry around adsorption site because palladium d‐orbitals rehybridize to maximize the overlap with NO orbitals (mainly the antibonding π*). Thus, the overall energetic effect of NO adsorption is the result of two competing processes: lowering of the total energy through tighter bonding with NO and rising the energy due to cluster deformation. The Pd~n~–NO bond creation is governed by electron transfer from Pd–d orbitals into the NO π*. As a result, the Pd cluster becomes locally demagnetized (with total magnetic moment of 1 μ~B~ located at Pd atoms not connected to NO) and the NO molecule is activated: the N–O bond length is increased and the vibration frequency is redshifted. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009
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