What is the Origin of Positional Fluctuation of Spectral Features: True Frequency Shift or Relative Intensity Changes of Two Overlapped Bands?

Ryu, Soo Ryeon; Noda, Isao; Jung, Young Mee

doi:10.1366/000370210792434396

Cited by 77 publications

(41 citation statements)

References 23 publications

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“…In the spectra collected after the fourth (t = 101 min) and the fifth pulses (t = 166 min), an increase in the intensity of the absorption bands associated to superficial sulfates/sulfites can be observed, accompanied by a shift from 1372 to 1381 cm 1 and from 1065 to 1052 cm 1 , respectively. The observed shift may be explained either by the combined effect of two overlapping bands that change in relative intensity or by a pure frequency shift of a single band induced by the change in the strength of molecular interactions 52 . Furthermore, a shoulder appears at 1205 cm 1 , associated with the formation of bulk-like sulfate species 18,26,31,50,51 .…”

Section: Analysis Of Stem Imagesmentioning

confidence: 99%

Mechanisms behind sulfur promoted oxidation of methane

Bounechada

Fouladvand

Kylhammar

et al. 2013

Phys. Chem. Chem. Phys.

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The promoting effect of SO2 on the activity for methane oxidation over platinum supported on silica, alumina and ceria has been studied using a flow-reactor, in situ infrared spectroscopy and in situ high-energy X-ray diffraction experiments under transient reaction conditions. The catalytic activity is clearly dependent on the support material and its interaction with the noble metal both in the absence and presence of sulfur. On platinum, the competitive reactant adsorption favors oxygen dissociation such that oxygen self-poisoning is observed for Pt/silica and Pt/alumina. Contrarily for Pt/ceria, no oxygen self-poisoning is observed, which seems to be due to additional reaction channels via sites on the platinum-ceria boundary and/or ceria surface considerably far from the Pt crystallites. Addition of sulfur dioxide generally leads to the formation of ad-SO(x) species on the supports with a concomitant removal and/or blockage/rearrangement of surface hydroxyl groups. Thereby, the methane oxidation is inhibited for Pt/silica, enhanced for Pt/alumina and temporarily enhanced followed by inhibition after long-term exposure to sulfur for Pt/ceria. The observations can be explained by competitive oxidation of SO2 and CH4 on Pt/silica, formation of new active sites at the noble metal-support interface promoting dissociative adsorption of methane on Pt/alumina, and in the case of Pt/ceria, formation of promoting interfacial surface sulfates followed by formation of deactivating bulk-like sulfate species. Furthermore, it can be excluded that reduction of detrimental high oxygen coverage and/or oxide formation on the platinum particles through SO2 oxidation is the main cause for the promotional effects observed.

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Section: Analysis Of Stem Imagesmentioning

confidence: 99%

Mechanisms behind sulfur promoted oxidation of methane

Bounechada

Fouladvand

Kylhammar

et al. 2013

Phys. Chem. Chem. Phys.

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“…SMCR result of the temperature-dependent IR spectra of ethylene glycol was previously reported 3 The maximum position ν max of the composite peak can be obtained from the experimentally observed spectra. Combined with the band positions ν 1 and ν 2 of the pure component spectra obtained from SMCR, (ν 1 -ν max )/(ν 1 -ν 2 ) was calculated.…”

Section: -5mentioning

confidence: 84%

“…It is in good agreement with our previous results that there are two distinct species, probably the hydrogen bonded and either nonhydrogen bonded or substantially weakly bonded ethylene glycol, which change their relative populations with temperature. 3 …”

Section: -5mentioning

confidence: 99%

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Relationship between Infrared Peak Maximum Position and Molecular Interactions

Ryu¹,

Noda

Jung

2011

Bulletin of the Korean Chemical Society

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We explored the interpretation of the well-accepted correlation between the apparent peak maximum position shift and extent of molecular interactions, like hydrogen bonding and dipole-dipole interactions, based on the overlapped multiple band model. The simulation of two overlapped Lorentzian bands was carried out to interpret how the maximum position of a composite peak relates to the relative contributions of two species representing the different levels of molecular interactions, i.e., free (or very weekly bound) vs. strongly bound. To demonstrate the validity of our interpretation of the origin of the peak position shift, the temperaturedependent IR spectra of ethylene glycol were also analyzed. It was found through the analysis of simulated and experimental spectra that the apparent peak shift in certain case can be safely interpreted as the measure of the strength of hydrogen bonding. The result of this study gives a new insight to interpret molecular interactions probed by vibrational spectroscopy.Key Words : Frequency shifts, Overlapped bands, Self-modeling curve resolution (SMCR), Hydrogen bonding, Molecular interaction IntroductionThe extent of bathochromic shift of certain IR peaks under the influence of temperature or solution composition has been historically used as a convenient metric to characterize the degree or strength of specific molecular interactions, such as hydrogen bonding and dipole-dipole interactions. Pimentel and Sederholm published a classical paper on the "empirical correlation" between shift of stretching frequencies and hydrogen bond distances in solid crystals. 1Similarly, the energy of hydrogen bonds has been estimated with the equation developed by Struszczyk based on the extent of peak position shift.2 The success of such empirical correlation provided the support for the so-called single band position shift model, where the position of the vibrational frequency of a single absorption band associated with a specific species under the influence of molecular interaction gradually changes as temperature or concentration of a mixture is changed.Recently, we have reported that many, if not most, of the bathochromic shift of IR peaks of liquid samples may be explained by the relative intensity changes of closely overlapped multiple bands, representing the relative population of discrete species in different state of interactions, which contribute to the absorption at fixed vibrational frequencies. [3][4][5][6] In this model, the individual vibrational frequency does not gradually shift with molecular environment, but their relative contribution changes as environmental factors, like temperature or concentration of a mixture is varied.In this study, we explore the interpretation of the wellaccepted correlation between the apparent peak maximum position shift and the extent of molecular interactions, like hydrogen bonding and dipole-dipole interactions, based on the overlapped multiple band model. To see how the maximum position of a composite peak relates to the relative contributio...

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“…18 It was found that the spectral dataset containing a real band frequency shift requires substantially more principal components (PCs) than normal PCA situations to adequately capture the detailed intensity variations arising from the nonlinear effect. This is because the shifting peak cannot be described as a simple linear combination of other peaks located at different frequencies.…”

Section: Introductionmentioning

confidence: 99%

Moving Window Principal Component Analysis for Detecting Positional Fluctuation of Spectral Changes

Ryu¹,

Noda²,

Jung³

2011

Bulletin of the Korean Chemical Society

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In this study, we proposed a new promising idea of utilizing moving window principal component analysis (MWPCA) as a sensitive diagnostic tool to detect the presence of peak position shift. In this approach, the moving window is constructed from a small data segment along the wavenumber axis. For each window bound by a narrow wavenumber region, separate PCA analysis was applied. Simulated spectra with complex spectral feature variations were analyzed to explore the possibility of MWPCA technique. This MWPCA-based detection of the peak shift, potentially coupled with 2D correlation analysis to provide additional verification, may offer an attractive solution.

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What is the Origin of Positional Fluctuation of Spectral Features: True Frequency Shift or Relative Intensity Changes of Two Overlapped Bands?

Cited by 77 publications

References 23 publications

Mechanisms behind sulfur promoted oxidation of methane

Mechanisms behind sulfur promoted oxidation of methane

Relationship between Infrared Peak Maximum Position and Molecular Interactions

Moving Window Principal Component Analysis for Detecting Positional Fluctuation of Spectral Changes

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