Molecular interactions and cooperativity in coadsorption:

Skelton, D.; Wei, D.H.; Kevan, S. D.

doi:10.1016/0039-6028(96)00510-9

Cited by 7 publications

(2 citation statements)

References 18 publications

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“…Nevertheless, interestingly marked differences in the CO-CO and NO-NO interactions on Pt(100) in UHV have been determined from calorimetry, 16 and the presence of weakly attractive CO/NO interactions on Pt(111) has been implied from desorption kinetic data. 35 The occurrence of molecularly intermixed CO/NO adlayers has also been deduced, primarily from vibrational spectroscopy, on several low-index Pt-group surfaces in UHV, 1a such as Pt(100), 36 even though the analyses are less quantitative than for the present system. We have recently made a similar structural deduction for CO/NO coadsorption on Pt(100) in aqueous solution, 5 as well as on Pt(111), Rh(100), and Pd(111).…”

Section: Concluding Remarks: Structural Implicationsmentioning

confidence: 84%

“…Unfortunately, there is little information available regarding such interaction terms, especially for mixed coadsorbates. Nevertheless, interestingly marked differences in the CO−CO and NO−NO interactions on Pt(100) in UHV have been determined from calorimetry, and the presence of weakly attractive CO/NO interactions on Pt(111) has been implied from desorption kinetic data …”

Section: Concluding Remarks: Structural Implicationsmentioning

confidence: 99%

See 1 more Smart Citation

Infrared Spectroscopy of Mixed Nitric-Oxide−Carbon-Monoxide Adlayers on Ordered Iridium(111) in Aqueous Solution: A Model Study of Coadsorbate Vibrational Interactions

et al. 1998

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In-situ infrared reflection−absorption spectra are reported for mixed nitric-oxide−carbon-monoxide adlayers along with the constituent chemisorbates separately as a function of coverage on ordered Ir(111) at 0.4−0.45 V vs standard hydrogen electrode in aqueous 0.1 M HClO4, with the objective of assessing the composition-dependent nature of the coadsorbate vibrational interactions. This substrate−coadsorbate combination provides an informative model system since both chemisorbates appear to bind exclusively in atop (or near-atop) surface sites on the basis of their simple N−O (νNO) and C−O (νCO) vibrational fingerprints, and composition-dependent mixed adlayers can readily be formed via partial replacement of saturated irreversible adsorbed NO layers by exposure to dilute CO solutions. Increasing the CO coverage, θCO, both in the absence and presence of coadsorbed NO, yields marked progressive blueshifts in the νCO band frequency (ca. 2020−2075 cm-1), attributable chiefly to enhanced dipole−dipole coupling. While adsorption of NO alone exhibited virtually coverage (θNO)-independent νNO frequencies, ca. 1835 cm-1, indicative of chemisorbate island formation, dilution within mixed CO/NO adlayers yields progressive νNO redshifts (down to ca. 1790 cm-1). The composition-dependent νCO and νNO frequencies within the CO/NO adlayers are consistent with molecular intermixing, as supported by comparison with numerical simulations extracted from conventional dipole-coupling theory, although the observed nonlinear νCO−θCO dependence suggests the formation of locally enriched CO regions at intermediate compositions. Evidence supporting coadsorbate intermixing is obtained by comparing the composition-dependent CO and NO band absorbances with the dipole-coupling predictions. In particular, the presence of coadsorbed CO yields marked (up to 3-fold) decreases in the NO band absorbance, especially toward lower νNO values, which arise from band-intensity transfer to neighboring higher-frequency (CO) oscillators. Despite the large (ca. 250 cm-1) difference in νNO and νCO singleton frequencies, this striking effect is in approximate agreement with dipole-coupling theory, again presuming molecular CO/NO intermixing. The observed marked increases in the νCO bandwidth toward lower θCO values, along with pronounced asymmetric band shapes, are in good agreement with theoretical predictions that include stochastic fluctuations of the local adsorbate population density. Moreover, the larger intermediate-θCO νCO bandwidths observed in the presence of coadsorbed NO are also quantitatively accounted for on this basis in terms of coadsorbate intensity transfer. The more broad-based utility of such dipole-coupling analyses for elucidating local interactions within mixed adlayers is considered in light of these findings.

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