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Title:Observation of transient surface-bound intermediates by Interfacial Matrix Stabilization Spectroscopy (IMSS)
Author(s):Moore, David T
Contributor(s):Jarrah, Nina K
Subject(s):Matrix isolation (and droplets)
Abstract:Interfacial matrix stabilization spectroscopy is a new technique based on matrix isolation spectroscopy, but where a cryogenic matrix is deposited over the top of a film sample, in order to characterize interactions between the substrate and molecular dopants. The IMSS technique harnesses the well-established ability of cryogenic matrices to trap and stabilize transient species, although in this case it is applied to intermediates relevant to heterogeneous catalysis. In this proof-of-concept study, we present data for CO and O$_{2}$ reactants binding to TiO$_{2}$ and Au/TiO$_{2}$ nanoparticle films, where in the latter case the Au nanoparticles were created by de-wetting of a 22.5 nm overlayer at ~450 K. The films are first pre-saturated with CO at 40 K, then cooled to 20 K, at which point an argon matrix is deposited over the top of them. The spectra are then annealed in stages over a range of temperatures between 20 and 40 K. In all cases, the presence of the Ar matrix alters the appearance of the CO bands, revealing additional structure, such as a broad feature at 2150 \wn, which is typically attributed to CO interacting with OH groups on the TiO$_{2}$ surface, but is not observed at 40 K for these samples in the absence of the matrix. The interpretation is that the matrix induces a caging-effect that prevents molecules from desorbing from weak binding sites from which they would be "pumped away" in the vacuum chamber if the matrix were not present. PerhACS the most interesting feature of these spectra is a small but sharp band at 2112 \wn that appears ONLY when O$_{2}$ is added to the argon matrix as a dopant. This transient band grows in following annealing at 32 K, but then disappears upon annealing above 34 K, suggesting that it may correspond to a reactive intermediate. The band occurs for samples both with and without Au present on the TiO$_{2}$ surface, but shows a larger intensity in the latter case. Possible assignments for the observed band in light of previous studies from the literature will be discussed in detail.
Issue Date:2014-06-19
Publisher:International Symposium on Molecular Spectroscopy
Citation Info:Moore, D.T.; Jarrah, N.K. OBSERVATION OF TRANSIENT SURFACE-BOUND INTERMEDIATES BY INTERFACIAL MATRIX STABILIZATION SPECTROSCOPY (IMSS). Proceedings of the International Symposium on Molecular Spectroscopy, Urbana, IL, June 16-21, 2014. DOI: 10.15278/isms.2014.RI08
Rights Information:Copyright 2014 by the authors. Licensed under a Creative Commons Attribution 4.0 International License.
Date Available in IDEALS:2014-09-17

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