Surface-enhanced Infrared Absorption Spectroscopy Research Articles

Understanding the Enhanced Methanol Oxidation Reactivity on Sulfur-Organic Compound Decorated Pt Electrode in Alkaline Media

Due to the rapid increase in environmental and energy issues, it is required to replace fossil fuel-driven conventional internal combustion engines with an energy conversion system using sustainable fuels. Although fuel cell is one of the possible candidates due to its high efficiency, the storage and transportation of hydrogen fuel hinder its widespread use.1 To overcome this problem, hydrogen careers, hydrogen-rich liquid and solid-phase materials, have been proposed as alternative fuels for fuel cell systems. Among the hydrogen carriers, methanol is one of the promising candidates due to its low production cost and high energy density. However, the slow kinetics of the methanol oxidation reaction (MOR), which proceeds via a complex six-electron pathway, limits the overall efficiency of the direct methanol fuel cell (DMFC).2 Much effort has been put into improving the MOR activity, including the development of electrocatalyst by metal alloying and surface modification of the electrocatalyst by thiol derivatives.3 Here, we focused on using sulfur-organic compound copolymer synthesized from S8 and organic molecules as a surface modifier. We then explored the reaction mechanisms on Pt surface in the alkaline environment by tracking the surface-bound intermediates using in situ surface-enhanced infrared absorption spectroscopy (SEIRAS). We selected styrene as an organic component and synthesized sulfur-organic compound copolymer (poly(s-st)). Synthesized poly(s-st) was decorated on the Pt surface by simply immersing the electrode into the poly(s-st)-contained solution. Cyclic voltammogram and X-ray photoelectron spectroscopy confirm the surface modification of the Pt surface by poly(s-st), which was stable after 5 cycles of potential cycling in 0.1 M KOH electrolyte. The oxidation current at 0.78 V vs. RHE, which is related to the MOR, was more significant than the pristine Pt electrode, which confirms the improvement of the MOR activity by poly(s-st) modification. The degree of activity enhancement became more substantial with the increase in alkyl chain length of alcohol fuels (methanol < propanol < 1-butanol), suggesting the reason of the enhanced activity to be the hydrophobic interaction between phenyl group of a surface modifier and alkyl portion of alcohol fuels which could facilitate the fuel supply on Pt electrode. In order to support our hypothesis, we performed SEIRAS measurement, where we observed a peak corresponds to the site-blocking species at ca. 1500 cm-1 for pristine Pt surface, while no corresponding peak was observed for poly(s-st) modified Pt surface. We will discuss the changes in the surface reaction mechanism based on the direct observation of the reaction intermediates by SEIRAS. It will also be demonstrated that the holistic information about the nature of the adsorbed species can provide a strategy to design the surface modifier to tune the energetics of key reaction intermediates, leading to further improvements in electrocatalytic activity for the methanol oxidation reaction.[1] Z-F. Li et al. Electrochim. Acta. 2017, 228, 351–360.[2] C. Lamy et al. J Appl. Electrochem. 2001, 31, 799–809.[3] H. Zimmermann et al. Chem. Eur. J. 2000, 4, 592–599.

Asp22 drives the protonation state of the Staphylococcus epidermidis glucose/H+ symporter

The Staphylococcus epidermidis glucose/H+ symporter (GlcPSe) is a membrane transporter highly specific for glucose and a homolog of the human glucose transporters (GLUT, SLC2 family). Most GLUTs and their bacterial counterparts differ in the transport mechanism, adopting uniport and sugar/H+ symport, respectively. Unlike other bacterial GLUT homologs (for example, XylE), GlcPSe has a loose H+/sugar coupling. Asp22 is part of the proton-binding site of GlcPSe and crucial for the glucose/H+ co-transport mechanism. To determine how pH variations affect the proton site and the transporter, we performed surface-enhanced IR absorption spectroscopy on the immobilized GlcPSe We found that Asp22 has a pKa of 8.5 ± 0.1, a value consistent with that determined previously for glucose transport, confirming the central role of this residue for the transport mechanism of GlcPSe A neutral replacement of the negatively charged Asp22 led to positive charge displacements over the entire pH range, suggesting that the polarity change of the WT reflects the protonation state of Asp22 We expected that the substitution of the residue Ile105 for a serine, located within hydrogen-bonding distance to Asp22, would change the microenvironment, but the pKa of Asp22 corresponded to that of the WT. A167E mutation, selected in analogy to the XylE, introduced an additional protonatable site and perturbed the protonation state of Asp22, with the latter now exhibiting a pKa of 6.4. These studies confirm that Asp22 is the proton-binding residue in GlcPSe and show that charged residues in its vicinity affect the pKa of glucose/H+ symport.

Micro- and Nanoscale Spectroscopic Investigations of Threonine Influence on the Corrosion Process of the Modified Fe Surface by Cu Nanoparticles.

The work presents a comprehensive vibrational analysis of the process of adsorption of threonine (Thr) onto an Fe surface with deposited Cu nanoparticles (NPs) (of about 4–5 nm in size) in a corrosive environment. The application of surface-enhanced Raman spectroscopy (SERS) and surface-enhanced infrared absorption spectroscopy (SEIRA) provides the opportunity for detailed description of adsorption geometry of amino acid onto a metal surface. The combination of conventional infrared spectroscopy (IR) with atomic force microscopy (AFM) resulted in a nano-SEIRA technique which made it possible to provide a precise description of adsorbate binding to the metal surface. The studies presented confirmed that there is a very good correlation between the spectra recorded by the SERS, SEIRA, and nano-SEIRA techniques. Threonine significantly influenced the process of corrosion of the investigated surface due to the existing strong interaction between the protonated amine and carboxylate groups and the CuNPs deposited onto the Fe surface. In addition, the application of two polarization modulations (s and p) in nano-SEIRA allows subtle changes to be observed in the molecule geometry upon adsorption, with the carboxylate group of Thr being almost horizontally oriented onto the metal surface; whereas the amine group that contains nitrogen is oriented perpendicular to this surface.

Origin of a High Overpotential of Co Electrodeposition in a Room-Temperature Ionic Liquid.

Metal electrodeposition in room-temperature ionic liquids (RTILs) often shows high overpotentials. Although this is often explained by the formation of a negatively charged metal complex due to the coordination of RTIL anions and the hindrance of its close approach onto the negatively charged electrode, we propose an alternative model based upon surface-enhanced infrared absorption spectroscopy measurements under Co electrodeposition. We found that the anionic first layer exists on the negatively charged electrode, and its replacement with a cationic one and Co electrodeposition both begin at an identical onset potential. The correlation between the interfacial structure and the electrodeposition reaction that can be modified by additives indicated that the high overpotential can be mainly attributed to the restructuring of the characteristic interfacial multilayer structure stabilized by its charge order, which is required for the reorganization of solvent ions after the reduction of Co2+.

Sol–Gel and Electrospinning Synthesis of Silica–Hydroxyapatite–Silver Nanofibers for SEIRAS and SERS

Surface-enhanced Raman spectroscopy (SERS) and Surface-enhanced infrared absorption spectroscopy (SEIRAS) are both novel techniques favored by the excitation of surface plasmons onto metal nanostructures. The light emitted from the metal surface couples with the vibrational transitions of molecules in proximity, enhancing its spectral response and leading to more sensitive and effective spectroscopic analysis. The absence of inexpensive and reproducible substrates is among the major impediments to the accurate implementation and optimal performance of the technique. The development of a low-cost active substrate based on silica–hydroxyapatite through sol–gel synthesis and electrospinning is addressed in the present study. Fibers of 512 ± 199 nm diameter were produced after sintering at 1150 °C on the electrospun mats. The fibers are fixed to an indium tin oxide (ITO) glass base for electrodeposition with 10 and 20 mM AgNO3 at 1.5 and 3.3 V at different time periods. Electrodeposition produced silver nanorods and nanocubes on the fibers. The SERS and SEIRAS activity of each one of the nine supports was tested using pyridine 1 nM, comparing it with the spectrum of pyridine 1 mM. An enhancement factor of 2.01 × 106 for the band at 3335 cm−1 was obtained during a SEIRAS essay for the support doped for 2 min at 3.3 V with 10 mM silver nitrate solution. The highest SERS enhancement factor was 3.46 × 108, for the band at 1567 cm−1 in the substrate doped for 5 min at 1.5 V with silver nitrate solution at 10 mM. After testing both samples with 10−4 M violet crystal solution, no SERS enhancement factor was found, but higher band resolution in the spectra was observed.

Revisiting the Acetaldehyde Oxidation Reaction on a Pt Electrode by High-Sensitivity and Wide-Frequency Infrared Spectroscopy.

High-sensitivity and wide-frequency attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) is highly demanded in unraveling electrocatalytic processes at the molecular level. In this work, an in situ ATR-SEIRAS technique incorporating a micromachined Si wafer window, p-polarized infrared radiation, and isotope labeling is extended to revisit the acetaldehyde oxidation reaction (AOR) on a Pt electrode in an acidic medium. New spectral features in the fingerprint region are detected, including ω(C-H) at 1078 cm-1 and νas(C-C-O) at 919 cm-1 for adsorbed acetaldehyde and δ(O-C-O) at 689 cm-1 for adsorbed acetate, besides the other enhanced and clearly discriminated spectral signals at higher frequencies. Time-evolved and potential-dependent ATR-SEIRAS measurements together with advanced density functional theory calculations considering the coadsorption of CO and C2 species enable clarification of the structures and roles of surface C2 intermediates (η1(C)-acetyl and η1(H)-acetaldehyde), as reflected by the two bands at 1630 and 1663 cm-1, respectively, leading to updated pathways for the AOR on a Pt electrode.

Surface-Adsorbed CO as an Infrared Probe of Electrocatalytic Interfaces

Electrocatalytic interfaces enable chemical transformations of fundamental and technological significance that are challenging to achieve by other means. Examples include the selective oxidation of alcohols, the conversion of biomass, and the reduction of carbon dioxide. However, these electrocatalytic processes often show poor reaction selectivity and the catalysts are prone to deactivation. Key to improving the reaction selectivity and catalyst stability is a better molecular-level understanding of these complex interfaces. Generating these insights requires the probing of the catalytically active sites, the structure and dynamics of the electric double layer, and the evolution of these interfacial features under reaction conditions. Surface-enhanced infrared absorption spectroscopy (SEIRAS) is well-suited to provide these insights. In particular, the C≡O stretch mode of surface-adsorbed CO (COads) is sensitive to the applied potential, surface morphology, and electric double layer structure. COads is an intermediate in the reduction and oxidation of carbon monoxide and can be introduced as a spectator species during other reactions. Therefore, it is a powerful and broadly applicable infrared probe of the electrocatalytic interface. However, the complex dependence of the C≡O stretch spectra on the local environment of the COads probe renders the interpretation of the spectra a non-trivial task. On the basis of recent SEIRAS studies of C≡O stretch spectra of COads on various electrocatalysts, we discuss successful strategies for inferring key structural aspects of the interface from the spectra. We highlight pitfalls in the analysis and propose future experimental and theoretical advances that will be required to realize the full potential of this methodology. Further, we show how SEIRAS can be augmented with differential electrochemical mass spectrometry (DEMS) for the elucidation of interfacial structure-reactivity relationships.

Monoclonal antibody 4B1 influences the pKa of Glu325 in lactose permease (LacY) from Escherichiacoli: evidence from SEIRAS.

The monoclonal antibody 4B1 binds to a conformational epitope on the periplasmic side of lactose permease (LacY) of Escherichiacoli and inhibits H+ /lactose symport and lactose efflux under nonenergized conditions. At the same time, ligand binding and translocation reactions that do not involve net H+ translocation remain unaffected by 4B1. In this study, surface-enhanced infrared absorption spectroscopy applied to the immobilized LacY was used to study the pH-dependent changes in LacY and to access insitu the effect of the 4B1 antibody on the pKa of Glu325, the primary functional H+ -binding site in LacY. A small shift of the pK value from 10.5 to 9.5 was identified that can be corroborated with the inactivation of LacY upon 4B1 binding.

Pixeled metasurface for multiwavelength detection of vitamin D

AbstractThe steadily increasing demand for accurate analysis of vitamin D level,viameasurement of its best general marker, 25-hydroxyvitamin D (25(OH)D), pushes for the development of novel automated assays capable of working at very low concentrations. Here, we propose a plasmonic biosensor of 25(OH)D3 (calcifediol) based on surface-enhanced infrared absorption spectroscopy, which exploits the resonant coupling between plasmonic nanoantennas and vibrational excitation of small molecules. Specifically, our proposed platform features a large-area (several mm2) metasurface made of gold nanoantennas fabricated on a silicon substrate, comprising different macroregions (“pixels”) of area 500 × 500 µm2. In each pixel, the nanoantenna geometrical parameters are tuned so as to support localized surface plasmon resonances (and hence large field enhancements at the nanoscale) within different regions of the infrared spectrum. As a result, a single chip is capable of performing analysis from the region of functional groups to that of fingerprint. Two different designs are fabricatedviaelectron beam lithography, functionalized with a correlated antibody for the detection of 25(OH)D3, and characterizedviaFourier-transform infrared spectroscopy. Our experiments demonstrate the capability to detect a concentration as low as 86 pmol/L, and an amount of immobilized small molecules of 25(OH)D3 monohydrate (molecular weight: 418.65 g/mol) as low as 4.31 amol over an area of 100 × 100 µm2.

Reorganization of Interfacial Water by an Amphiphilic Cationic Surfactant Promotes CO2 Reduction.

The presence of cetyltrimethylammonium bromide (CTAB) near the surface of a Cu electrode promotes the electrochemical reduction of CO2 to fuels. CTAB increases the CO2 reduction rate by as much as 10× and decreased the HER rate by 4×, leading to ∼75% selectivity toward the reduction of CO2. Surface enhanced infrared absorption spectroscopy (SEIRAS) was used to probe the effects of CTAB adsorption on the structure of interfacial water and CO2 reduction intermediates. HER suppression was found to arise from the displacement of interfacial water molecules from CTAB adsorption within the double layer. The enhanced CO2 reduction rate can be correlated to an increased population of atop-bound CO and the emergence of a low frequency atop-CO band. These results unravel the role of additives in improving CO2-to-fuels electrocatalysis and establishing this as a powerful methodology for directing product selectivity.

Cuprous Oxide Cubic Particles with Strong and Tunable Mie Resonances for Use as Nanoantennas

The ability of plasmonic metal nanostructures (PMNs), such as silver and gold nanoparticles, to manipulate and concentrate electromagnetic fields at the nanoscale is the foundation for wide range of applications, including nanoscale optics, solar energy harvesting, and photocatalysis. However, there are inherent problems associated with plasmonic metals, such as high Ohmic losses and poorer compatibility with the conventional complementary metal–oxide–semiconductor (CMOS) microfabrication processes. These limitations inhibit the broader use of PMNs in practical applications. Herein, we report submicrometer cuprous oxide (Cu2O) cubic particles can exhibit strong electric and magnetic Mie resonances with extinction/scattering cross sections comparable to or slightly exceeding those of Ag particles. Using size- and shape-controlling particle synthesis techniques, optical spectroscopy, and finite-difference time-domain simulations, we show that the Mie resonance wavelengths are size- and shape-dependent and tunable in the visible to near-infrared regions. Therefore, submicrometer Cu2O cubic particles may potentially emerge as high-performance alternatives to PMNs. The strong electric and magnetic Mie-resonance-mediated nanoantenna attribute of the Cu2O cubic particles can be potentially used in a wide range of applications, including nanoscale optics, surface-enhanced Raman spectroscopy, surface-enhanced infrared absorption spectroscopy, photocatalysis, and photovoltaics.

Concentrating and activating carbon dioxide over AuCu aerogel grain boundaries

Alloys are active in CO2 electroreduction due to their unique electronic and geometric structures. Nevertheless, CO2 reduction selectivity is still low due to the low concentration of CO2 near the catalyst surface and the high energy barrier for CO2 activation. This paper describes an AuCu nanochain aerogel (NC-AuCu) with abundant grain boundaries (GBs) that promote the accumulation and activation of CO2 for further electrochemical reduction, employing in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy and density functional theory calculations. GBs can induce a strong local electric field to concentrate the electrolyte cations and thus accumulate CO2 near the catalyst surface. NC-AuCu exhibits a superior Faradaic efficiency of close to 100% for CO2 electroreduction to CO at an extremely low overpotential of 110 mV with a high CO partial current density of 28.6 mA cm-2 in a flow cell. Coupling with a Si solar cell to convert solar energy to CO, a very high conversion efficiency of ∼13.0% is achieved. It potentially provides broad interest for further academic research and industry applications.

Operando identification of site-dependent water oxidation activity on ruthenium dioxide single-crystal surfaces

Understanding the nature of active sites is central to controlling (electro)catalytic activity. Here we employed surface X-ray scattering coupled with density functional theory and surface-enhanced infrared absorption spectroscopy to examine the oxygen evolution reaction on RuO2 surfaces as a function of voltage. At 1.5 VRHE, our results suggest that there is an –OO group on the coordinatively unsaturated ruthenium (RuCUS) site of the (100) surface (and similarly for (110)), but adsorbed oxygen on the RuCUS site of (101). Density functional theory results indicate that the removal of –OO from the RuCUS site, which is stabilized by a hydrogen bond to a neighbouring –OH (–OO–H), could be the rate-determining step for (100) (similarly for (110)), where its reduced binding on (100) increased activity. A further reduction in binding energy on the RuCUS site of (101) resulted in a different rate-determining step (–O + H2O – (H+ + e−) → –OO–H) and decreased activity. Our study provides molecular details on the active sites, and the influence of their local coordination environment on activity. Understanding the nature of active sites is central to controlling the activity of a given catalyst. This work combines operando characterization and computational techniques to examine the oxygen evolution reaction mechanism on RuO2 surfaces.

(Invited) Nitrogen Electrochemical Reduction Reaction Pathway on Noble Metallic Surfaces

Nitrogen reduction reaction (NRR) has become a hot topic in recent years, since it allows the directly conversion of renewable electricity energy to chemical energy stored in ammonia, with the advantages of zero CO2 emission and potential energy saving. In this process, nitrogen molecules are reduced directly on the cathodic electrode, with ammonia as the final product. However, the achievements in this area are still far from meeting the requirements for its commercial application, majorly owing to the serious competing of the hydrogen evolution reaction (HER) on the cathodic electrocatalysts surfaces. Furthermore, this serious competing reaction significantly limits the nitrogen reduction reaction mechanism study on electrode surface, which is vital for the rational design of more advanced electrocatalysts.In this work, we employed surface-enhanced infrared absorption spectroscopy (SEIRAS) and differential electrochemical mass spectrometry (DEMS) to study the reaction mechanisms of nitrogen reduction on noble metal surfaces (Au, Pt, Ru, Rh). The N-N stretching (1109 cm-1) of the *N2Hy (3≤y≤4) was observed on Au surface, and the N=N stretching (~2000 cm-1) of the *N2Hx (0≤x≤2) was detected on Ru and Rh surface by surface-enhanced infrared absorption spectroscopy. In addition, the pulse signal of N2H2 (m/e = 29) was also detected with H2 on Rh surface by differential electrochemical mass spectrometry. Based on these results, we may deduce an overall NRR reaction pathway on metallic surfaces as depicted in Scheme 1. There is an equilibrium between the dissolution and adsorption of the nitrogen molecule in the three-phase interface (K0, K0’, and Kdiff). On the metallic catalyst surfaces, the nitrogen reduction may either follow a dissociative (dotted line) or an associative (solid line) pathway. The associative pathway mainly contains three procedures, involving two-electron transfer (k2), four-electron transfer (k3), and six-electron transfer (k4). On metallic surface, the exact reaction pathway that NRR follows on a certain metallic surface is determined by the rate determining step. For instance, if the energy barrier for N2H2 desorption is relatively lower than that of further reduction of N2H2, the NRR would follow a two-electron transfer procedure with N2H2 as the product, which would subsequently decompose into ammonia and nitrogen in the electrolyte (k7). The similar phenomenon would occur in the four-electron transfer procedure with N2H4 as the by-product. While in the dissociative pathway, only six-electron transfer procedure (k1) is involved with ammonia as the only product. After ammonia is formed on the metallic surfaces, there would be another equilibrium between the desorption of the ammonia from the surfaces into the electrolyte (Kdiff’) or the gas phase (K10’), and an ammonia dissolution equilibrium between the gas phase and the electrolyte (K10).Scheme 1. Electrochemical nitrogen reduction reaction pathway on metallic surfaces: associative pathway (solid line) and dissociative pathway (dotted line). Figure 1

Physicochemical Characterization of Daptomycin Interaction with Negatively Charged Lipid Membranes.

Daptomycin is known as an effective antibiotic lipopeptide which shows activity against the number of Gram-positive pathogens. Its primary target is the bacterial cell membrane. However, the detailed mechanism of daptomycin action is still subject to debate. In this paper, we have investigated the interactions between lipopeptide and model lipid films composed of negatively charged phosphatidylglycerols and cardiolipin. In order to evaluate the effect of daptomycin on the molecular organization and the properties of lipid assemblies, we have used surface pressure measurements and electrochemical methods combined with atomic force microscopy, quartz crystal microbalance, and surface-enhanced infrared absorption spectroscopy. Our results indicate that daptomycin interaction with the lipid membrane is complex. It involves daptomycin aggregation and partial insertion, which in turn affect the charge distribution on both sides of the membrane and may result in a gradient of water chemical potential. The latter can drive the flux of water across the membrane.

PH-Dependent Hydrogen and Water Binding Energies on Platinum Surfaces as Directly Probed through Surface-Enhanced Infrared Absorption Spectroscopy.

The origins of the pH-dependent kinetics of hydrogen evolution and oxidation reactions on Pt surfaces are unsolved dilemmas that have lasted for over half a century. In this study, surface-enhanced infrared absorption spectroscopy is applied to directly monitor the vibrational behaviors of adsorbed hydrogen atoms and interfacial water molecules on Pt surfaces in a wide pH window from 1.1 to 12.9. For the first time, we successfully measure the pH-dependent changes of hydrogen and water binding strength according to their vibrational wavenumbers, which are both monotonously weakened as the solution pH increases. Their changes are the net results of altered electrochemical interface environments and are important contributions to the pH-dependent hydrogen reaction kinetics. Our results add significant new insights into the role of interfacial environments on electrocatalysis.

A Spectroscopic Study of Electrochemical Nitrogen and Nitrate Reduction on Rhodium Surfaces.

Rh is a promising electrocatalyst for the nitrogen reduction reaction (NRR) given its suitable nitrogen-adsorption energy and low overpotential. However, the NRR pathway on Rh surfaces remains unknown. In this study, we employ surface-enhanced infrared-absorption spectroscopy (SEIRAS) and differential electrochemical mass spectrometry (DEMS) to study the reaction mechanism of NRR on Rh. N2 Hx (0≤x≤2) is detected with a N=N stretching mode at ≈2020 cm-1 by SEIRAS and a signal at m/z=29 by DEMS. A new two-step reaction pathway on Rh surfaces is proposed that involves an electrochemical process with a two-electron transfer to form N2 H2 and its subsequent decomposition in the electrolyte producing NH3 . Our results also indicate that nitrate reduction and the NRR share the same reaction intermediate N2 Hx .

A Spectroscopic Study of Electrochemical Nitrogen and Nitrate Reduction on Rhodium Surfaces

AbstractRh is a promising electrocatalyst for the nitrogen reduction reaction (NRR) given its suitable nitrogen‐adsorption energy and low overpotential. However, the NRR pathway on Rh surfaces remains unknown. In this study, we employ surface‐enhanced infrared‐absorption spectroscopy (SEIRAS) and differential electrochemical mass spectrometry (DEMS) to study the reaction mechanism of NRR on Rh. N2Hx (0≤x≤2) is detected with a N=N stretching mode at ≈2020 cm−1 by SEIRAS and a signal at m/z=29 by DEMS. A new two‐step reaction pathway on Rh surfaces is proposed that involves an electrochemical process with a two‐electron transfer to form N2H2 and its subsequent decomposition in the electrolyte producing NH3. Our results also indicate that nitrate reduction and the NRR share the same reaction intermediate N2Hx.

Unveiling the molecule-plasmon interactions in surface-enhanced infrared absorption spectroscopy.

Nanostructure-based surface-enhanced infrared absorption (SEIRA) spectroscopy has attracted tremendous interest as an ultrasensitive detection tool that supplies chemical-fingerprint information. The interactions between molecular vibrations and plasmons lead to not only the enhancement of spectral intensity, but also the distortion of spectral Lorentzian lineshapes into asymmetric Fano-type or more complicated lineshapes in the SEIRA spectra; this effect hampers the correct readout of vibrational frequencies and intensities for an accurate interpretation of the measured spectra and quantitative analysis. In this work, we investigate the Fano interference between molecular vibrations and plasmons based on exact electrodynamic simulations and theoretical models. We report that, even if the molecular vibrational energy is equal to the plasmon resonant energy, the molecule–nanostructure distance-dependent dipole–dipole interactions, the plasmon-mediated coherent intermolecular interactions and the decay rates of plasmons have a significant impact on the SEIRA lineshapes. This study paves the way for controllable Fano interference at the nanoscale and more studies on plasmon-dressed molecular electronic or vibrational excited states.

Microsecond Resolved Infrared Spectroelectrochemistry Using Dual Frequency Comb IR Lasers.

A dual infrared frequency comb spectrometer with heterodyne detection has been used to perform time-resolved electrochemical attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS). The measurement of the potential dependent desorption of a monolayer of a pyridine derivative (4-dimethylaminopyridine, DMAP) with time resolution as high as 4 μs was achieved without the use of step-scan interferometry. An analysis of the detection limit of the method as a function of both time resolution and measurement coadditions is provided and compared to step-scan experiments of an equivalent system. Dual frequency comb spectroscopy is shown to be highly amenable to time-resolved ATR-SEIRAS. Microsecond resolved spectra can be obtained with high spectral resolution and fractional monolayer detection limits in a total experimental duration that is 2 orders of magnitude less than the equivalent step-scan experiment.