Interactions of nitric oxide molecules with pure and oxidized silver clusters Agn±/AgnO± (n=11–13): A computational study

Abstract

In this work, we have studied, within density functional theory, the interaction of NO with pure and oxidized silver clusters, both anionic and cationic, composed from 11 to 13 Ag atoms. In that size interval, shell closing effects are not expected, and structural and electronic odd–even effects will determine the strength of interaction. First, we obtained that species [Formula: see text] and Ag nO± with odd number of electrons ( n = 12) adsorb NO with higher energy than their neighbors ( n = 11 and 13). This result is in agreement with the facts observed in recent mass spectroscopy measurements, which were performed, however, at finite temperature. The adsorption energy is about twice for oxidized clusters compared to pure ones and higher for anions than for cations. Second, the adsorption of another NO molecule on Ag nNO± forms [Formula: see text], with the dimer (NO)2 in cis configuration, and binding the two N atoms with two neighbor Ag atoms. The n = 12 species show the higher adsorption energy again. Third, in the absence of reaction barriers, all complexes [Formula: see text] dissociate spontaneously into Ag nO± and N2O, except the n = 12 anion. The maximum high barrier along the dissociation path of [Formula: see text] is about 0.7 eV. Further analysis of projected density of states for [Formula: see text] (x = 0, 1, 2) molecules shows that bonding between NO and Ag clusters mainly occurs in the energy range between −3.0 and 3.0 eV. The overlap between 4 d of Ag and 2 p of N and O is larger for [Formula: see text] than for neighbor sizes. For n = 12, the d bands are close to the (NO)2 2 π orbital, leading to extra back-donation charge from the 4 d of Ag to the closer 2 π orbital of (NO)2.