Infrared Emission Spectroscopy Research Articles

Classification of black plastic types by hyperspectral imaging based on long-wave infrared emission spectroscopy

Identification of black plastics poses a significant challenge in recycling due to the absorptive nature of carbon black additives. This work introduces a method where hyperspectral imaging in the long-wave infrared regime is used to distinguish between twelve samples of commercially available black plastics encompassing nine distinct polymer types. The spectral scanner comprises a scanning Fabry-Pérot interferometer and a thermal camera based on an uncooled microbolometer detector sensitive to wavelengths from 8 μm to 15 μm. A principal component model is combined with k-nearest neighbors to differentiate between plastic samples in hyperspectral images. The model successfully classifies five (PET, POM, PMMA, PA6, and PA66) out of nine black polymers, and the overall accuracy of the model is A=73.1 %.

Reconstruction of Mars 2020 Backshell Radiative Heating via Infrared Emission Spectroscopy of CO2/N2/Ar Shockwaves

A test series was performed in the Electric Arc Shock Tube (EAST) facility with the aim of reproducing flight conditions encountered during the Mars 2020 mission entry into the Mars atmosphere. For this test series, the EAST facility was instrumented with two spectrometers for optical emission spectroscopy (OES) measurements and three mid-infrared lasers for tunable diode laser absorption spectroscopy (TDLAS). This paper focuses on the spectrally and spatially resolved radiance measured with OES. Conditions were chosen to achieve similarity to backshell radiative heating measured with the MEDLI2 heat flux gauges near and after the time of peak heating. Comparisons were made against two candidate kinetic models for Mars entry. Below 2.7 km/s, the chemistry is effectively frozen, with measurements being above both models and CEA predictions. It is shown that taking into account shock deceleration in the tube explains most of the discrepancy between measured and frozen radiance. For velocities above 2.7 km/s, the data lies between the two models. However, adjusting for shock deceleration indicates that one of the models may be preferred for predicting CO2 dissociation. Finally, comparisons between OES and TDLAS data are made and show a good agreement on the measured temperature and CO2 number density profiles, typically within 10 and 5%, respectively. A good agreement is also observed for the radiance that would be inferred based upon the quantities measured by TDLAS.

Static and kinetic study of the structure and dynamics of vitreous silica at high temperatures by infrared emission spectroscopy

Emissivity spectra of amorphous silica have been acquired in a wide range of temperatures: from 4 K to more than 2500 K in static isothermal conditions, and from 2500 K to 600 K in kinetic free-cooling conditions. A fitting procedure allows extracting the temperature dependence of the dielectric function in the range of vibrational frequencies. Both sets of data are equivalent for a quantitative study of the structure of this model glass, despite the lower resolution and signal-to-noise ratio of the rapid-scan measurements. The results present clear changes at a special temperature near the α→β transition temperature for crystalline quartz. Similarly, simple relations between the intensities of the modes are found at the glass transition. This study provides insight into the structure and dynamics of vitreous silica at high temperature and proves that rapid-scan infrared emission spectroscopy is a viable analytical technique for the study of materials in non-equilibrium conditions.

Spatially Heterogeneous Chemistry Observed using NIRTI on SOFC Anodes

Carbon formation remains the primary degradation mechanism for solid oxide fuel cells (SOFCs) operating on carbonaceous fuels. The mechanisms for the remediation of carbon (C) induced degradation via electrochemical gasification and reforming using O2(g) and H2O(g) was studied using Near Infrared Thermal Imaging (NIRTI), Fourier Transform Infrared Emission Spectroscopy (FTIRES), chronoamperometry/chronopotentiometry (CA/CP), and mass spectrometry (MS). Carbon removal follows a stepwise mechanism, first oxidizing surface carbon to CO(g), and subsequently to CO2(g). CO(g) oxidation requires a catalytic surface to form CO2 which plays a key role in removing C via the reverse Boudouard chemistry. NIRTI reveals spatially heterogenous chemistry and suggests a specific role of surface oxygen species. These species form from dissociative adsorption and non-faradaic oxide flux through the electrolyte, as well as O2 transport limited processes occurring due to high O2 utilization. C removal from electrochemical oxidation and steam spatially homogeneous compared to O2, due in part to the respective active surface species, and their respective transport limitations. Under O2 C removal is appears incomplete, despite electrochemical results. These experiments clarify the mechanisms responsible for remediation of C on SOFC anodes and highlight the need of spatially resolved techniques to study SOFCs under operating conditions.

Comparison of Carbon Deposition and Removal from Ni-YSZ and Ni-BCZY Composites Using Operando Optical Methods

Solid oxide fuel cells (SOFCs) are attractive devices for power generation because they can operate with a variety of fuels, including H2, hydrocarbon fuels, biogas, and syngas. Conventional SOFC anode composites comprised of Ni-YSZ (YSZ = yttria-stabilized zirconia), however, suffer from performance degradation due to surface accumulation of carbon from hydrocarbon cracking. Alternative electrolyte materials such as yttria-doped barium cerate/zirconate mixtures (BCZY) offer the promise of reduced carbon formation over the Ni-BCZY electrode and lower operating temperatures by the conduction of protons instead of oxide ions. In this study, 50%-50% Ni-8YSZ and 50%-50% Ni-BCZY27 composites were exposed to CH4 in the absence and presence of either CO2 or H2O. The degree of carbon deposition and mechanism of carbon removal in the absence of fuel was estimated in the presence of steam using operando Fourier transform infrared emission spectroscopy (FTIRES) and near-infrared thermal imaging (NIRTI) at 750 °C. Upon exposure to each fuel condition, carbon removal using steam results in more CO2 + CO product formation from Ni-8YSZ implying more carbon formation on Ni-8YSZ compared to Ni-BCZY27. Carbon removal of cells exposed to CH4 alone indicate limited formation and fast depletion of CO over Ni-BCZY27; depletion of CO2, however, happens more slowly. Depletion of CO and CO2 in the Ni-8YSZ system happens more gradually suggesting the deposition of carbon over Ni-BCZY27 occurs less readily and its removal is more facile through gasification. Interestingly, the cracking of CH4 over Ni-8YSZ is accompanied by a larger degree of cooling compared to Ni-BCZY27 whereas both dry and wet reforming result in similar cooling over Ni-8YSZ and Ni-BCZY27. The results will be discussed in the context of recent work using operando spectroscopies to characterize CH4 fuel utilization in Ni-8YSZ based SOFCs in the absence and presence of various reformers.

Quantification of gas, ash, and sulphate aerosols in volcanic plumes from open path Fourier transform infrared (OP-FTIR) emission measurements at Stromboli volcano, Italy

Field-portable Open Path Fourier Transform Infrared (OP-FTIR) spectrometers can be used to remotely measure the composition of volcanic plumes using absorption spectroscopy, providing invaluable data on total gas emissions. Quantifying the temporal evolution of gas compositions during an eruption helps develop models of volcanic processes and aids in eruption forecasting. Absorption measurements require a viewing geometry which aligns infrared source, plume, and instrument, which can be challenging. Here, we present a fast retrieval algorithm to estimate quantities of gas, ash and sulphate aerosols from thermal emission OP-FTIR measurements, and the results from two pilot campaigns on Stromboli volcano in Italy in 2019 and 2021. We validate the method by comparing time series of SO2 slant column densities retrieved using our method with those obtained from a conventional UV spectrometer, demonstrating that the two methods generally agree to within a factor of 2. The algorithm correctly identifies ash-rich plumes and gas bursts associated with explosions and quantifies the mass column densities and particle sizes of ash and sulphate aerosols (SA) in the plume. We compare the ash sizes retrieved using our method with the particle size distribution (PSD) of an ash sample collected during the period of measurements in 2019 by flying a Remotely Piloted Aircraft System into the path of a drifting ash plume and find that both modes of the bimodal PSD (a fine fraction with diameter around 5–10 μm and a coarse fraction around 65 μm) are identified within our datasets at different times. We measure a decrease in the retrieved ash particle size with distance downwind, consistent with settling of larger particles, which we also observed visually. We measure a decrease in the SO2/SA ratio as the plume travels downwind, coupled with an increase in measured SA particle size (range 2–6 μm), suggesting rapid hygroscopic particle growth and/or SO2 oxidation. We propose that infrared emission spectroscopy can be used to examine physical and chemical changes during plume transport and opens the possibility of remote night-time monitoring of volcanic plume emissions. These ground-based analyses may also aid the refinement of satellite-based aerosol retrievals.

Aromatic and Acetylenic C-H or C-D Stretching Bands Anharmonicity Detection of Phenylacetylene by UV Laser-Induced Vibrational Emission.

The anharmonic infrared (IR) emission spectra of phenylacetylene C6H5CCH and an isotopologue C6H5CCD induced by 193 nm UV excitation have been investigated in the gas phase. The study has been operated with a homemade IR spectrometer enabling to record time- and wavelength-resolved spectra between 2.5 and 4.5 μm, emitted all along the collisional cooling. The analysis is supported by a kinetic Monte Carlo simulation in the vibrational harmonic approximation. For both species, the anharmonic shifts of the acetylenic C-H or C-D stretching modes and the aromatic C-H stretching modes are studied for band positions and bandwidths in terms of the internal energy. For C6H5CCD, the internal energy dependence of the emission intensity band ratio is investigated and rationalized. This work demonstrates the potential of time-resolved IR emission spectroscopy to explore anharmonicity of astrophysically relevant molecules.

Time-resolved fourier transform infrared emission spectroscopy of NH radical in the X3Σ− ground state

The NH radical is an extremely important specie in nitrogen chemical reaction networks, in the interstellar medium and atmospheric chemistry. Time resolved Fourier transform spectroscopy technique in the frequency range 10–13 µm has been applied for the measurement of a pure rotational spectrum of the NH free radical (NH) in the ground X3Σ− electronic state. Twelve high N (26–29) triplet-resolved pure rotation lines of NH were experimentally observed in the laboratory and compared with satellite ACE (Atmospheric Chemistry Experiment) solar data. In addition, discharge-generated vibration-rotation NH radical bands in the spectral range 1923–3571 cm−1 have been measured with a microsecond time resolution and spectral resolution of 0.02 cm−1. The spectra of the NH radical have been studied in two experimental arrangements. Firstly, in a pulsed positive column discharge of pure hydrogen-nitrogen mixture and secondly, in a discharge of nitrogen-ammonia mixture in the presence of argon buffer gas. Both production methods are described and compared. The population analysis of the experimental spectra was performed via modelling using the accurate MoLLIST line lists for NH. It was shown that laboratory data can be well reproduced by use of a mixture of the local-thermal-equilibrium (LTE) and non-LTE models corresponding to high temperatures (up to 8000 K and up to 6000 K rotational).

CO2 number density measurement in a shock tube with preheated carbon surface

The interaction between a heated carbon-based material and high-temperature air may produce ablation gas species such as CO2, affecting heat transfer onto the surface of a thermal protection system. The prediction of ablation gas production is critical for heat flux prediction and the design of a thermal protection system. In this study, we present a system that measures the number density of CO2 formed by the gas–surface interaction between a hot carbon surface and high-temperature gas. The heated carbon wall is exposed to high-temperature air by using a shock tube and surface heating model. The surface temperature of the carbon wall is measured using two-color ratio pyrometry. The number density of CO2 is predicted by performing numerical calculations for the shock tube flow with gas–surface interaction modeling. The number density of CO2 molecules is measured using infrared emission spectroscopy. The measured CO2 number density is 9.60 × 1023 m−3 at an area-weighted average surface temperature of 1212 K. The measured number density matches the predicted value within an error of 6%. The proposed system is applicable for CO2 number density measurement under various gas–surface interaction conditions, and it can be used for the investigation of ablative gas production and numerical research on gas–surface interactions.

Reactions of OH and OD radicals with ethanethiol and diethylsulfide: Branching ratio and vibrational energy disposal for the product water molecules

Reactions of OH and OD radicals with C 2 H 5 SH and (C 2 H 5 ) 2 S were studied by Fourier-transform infrared emission spectroscopy of the water product molecules from a fast-flow reactor. Vibrational excitation of the H 2 O, HOD and D 2 O product molecules was determined by computer modeling of the chemiluminescence spectra. Spectra of the abstraction of H-atom from the ethyl group (C-H) and sulfur atom (S-D) were separated using deuterated reactant, C 2 H 5 SD. The branching ratio was found to be 0.24 ± 0.05 (C-H):0.76 (S-D) both for OH and OD reactants. For the OH + C 2 H 5 SH reaction the branching fraction for the (C-H) channel of 0.25 ± 0.06 was obtained. Vibrational energy disposal for S-H abstraction is similar to that for the reaction with CH 3 SH, whereas abstraction from the ethyl group demonstrates higher bending excitation than abstraction from the methyl group of CH 3 SH. A similar trend was found for abstraction from the ethyl and methyl groups of (C 2 H 5 ) 2 S and CH 3 SCH 3 .

Radiative Relaxation of Gold Nanorods Coated with Mesoporous Silica with Different Porosities upon Nanosecond Photoexcitation Monitored by Time-Resolved Infrared Emission Spectroscopy.

Gold nanorods (AuNRs) have been widely used in photothermal conversion, and a coating of silica (SiO2) provides higher thermal stability, better biocompatibility, and versatile chemical functionalization. In this work, two gold nanorods coated with surfactant-templated mesoporous silica layers of the same thickness but different porosities, and thus different specific surface areas, were prepared. Upon irradiation with 1064 nm nanosecond pulsed laser, the transient infrared emissions of AuNR@SiO2 enveloped the stretching mode of the Si-O-Si bridge (1000-1250 cm-1), the bending mode of adsorbed H2O (1600-1650 cm-1) within the mesoporous silica layer, and blackbody radiation, in terms of an underlying broad band (1000-2000 cm-1) probed with a step-scan Fourier transform spectrometer. The mesoporous silica shell and the adsorbed H2O gained populations of their vibrationally excited states, and the whole AuNR@SiO2 was heated up via the photothermal energy of the core AuNRs. An average temperature after 5-10 μs within 80% of the emission intensity was ca. 200 °C. The decay of the emission at 1000-1250 and 1500-1750 cm-1 was both accelerated, and the blackbody radiation components were negatively correlated with the porosity of the mesoporous silica layer. Higher porosity of the mesoporous silica layer was associated with more effective depopulation of the vibrationally excited states of the silica layers on the AuNRs via the nonradiative thermal conduction of the adsorbed H2O, since H2O has a larger thermal conduction coefficient than that of silica, in concomitance with the accelerated emission kinetics. This work unveils the roles of the porosity, capping materials, and entrapping molecules of a core-shell nanostructure during the thermalization after photoexcitation.

Silver nanoparticles on UiO-66 (Zr) metal-organic frameworks for water disinfection application

Drinking water disinfection is an essential process to assure public health all over the world. In this study, silver nanoparticles (AgNPs) on UiO-66 (Zr) Metal-Organic Frameworks (Ag@UiO-66) is proposed as a potential water disinfection strategy. AgNPs are synthesized using polyvinyl pyrrolidone (PVP) as stabilizing agent, and sodium borohydride as reducing agent are subsequently embedded on UiO-66, a high-stability organometallic framework. The effect of premixing time, reaction time and reactant concentration on the loading rate of AgNPs on UiO-66 was investigated. The maximum load rate of AgNPs on UiO-66 could reach 13% when the premixing time is 3h, the reaction time is 45min and the concentration of AgNO3 is 10μg/mL. The formation of AgNPs loaded on UiO-66 was observed and confirmed with ultraviolet and visible spectrophotometry (UV-Vis), scanning electron microscopy (SEM), infrared emission spectroscopy (IES) and X-ray diffraction (XRD) analysis. Ag@UiO-66 exhibited strong antibacterial activity against both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus, with minimum inhibitory concentrations (MIC) of 64 and 128μg/mL, respectively. The germicidal efficacy of Ag@UiO-66 enhanced significantly as the temperature rose from 4°C to 37°C. The results indicate that Ag@UiO-66 is potential candidate as a feasible water disinfection material.

Operando optical studies of solid oxide fuel cells operating on CO and simulated syngas fuels

Solid oxide fuel cells (SOFCs) are attractive devices for combined power and heat generation because they can operate with a variety of fuels. Syngas (CO + H2) is particularly attractive but many questions remain about its behavior on SOFC anodes including the relative oxidation efficiencies of CO and H2 and tendency to form carbon deposits. In this report, operando spectroelectrochemical measurements, including infrared emission spectroscopy, near infrared thermal imaging, and vibrational Raman scattering, combined with spectrochronopotentiometry, are performed using anode-supported SOFCs operating with simulated syngas at 800 °C. Results quantify the fate of syngas over Ni-YSZ anodes in SOFCs related to their performance. SOFCs operating with simulated syngas mixtures are compared with those for H2 and CO used separately. Thermal imaging shows more SOFC anode heating for H2-rich syngas than for operating on CO or H2 alone. We attribute this result to carbon gasification by water that is produced by H2 oxidation. Raman spectra together with spectrochronopotentiometry experiments illustrate that carbon is not observed on the anode surface at 800 °C – although it is at 750 °C and 700 °C – yet carbon is likely present in the spectroscopically inaccessible, electrochemically active region at the electrolyte-electrode interface.

Beyond the rule of transition state: Identification of roaming routes in some cases of carbonyl compounds

AbstractThis account focuses on photodissociation of carbonyl compounds to verify a so‐called roaming route, alternative to those passing through a transition state (TS) invoked in the realm of the kinetics of elementary chemical processes. Such a roaming route bypasses the minimum energy path but produces the same molecular products. The photodissociation of the carbonyl compounds of study includes methyl formate (HCOOCH3), formic acid (HCOOH), and aliphatic aldehydes (RCOH, RH, CH3, and large alkyl group). Methyl formate and formic acid were promoted to the excited state, followed by internal conversion via a conical intersection. Then, the energetic precursor dissociated to fragments, which proceeded along either TS or roaming path. As the excitation energy increases, the roaming fraction in methyl formate is significantly interfered with by an open channel of triple fragmentation (H + CO + CH3O), whereas such a channel may not occur in formic acid even at an excitation wavelength of 193 nm. As a distinct roaming type, aliphatic aldehydes are found to possess the structure of the roaming saddle point comprising two moieties weakly bound at a distance. The energy difference between the TS barrier and the roaming saddle point is indicative of the extent for the roaming contribution. The roaming route becomes increasingly dominant when the aliphatic aldehyde is larger. Experimentally, ion imaging was employed to visualize the rotational‐level dependence of the roaming route, while time‐resolved Fourier‐transform infrared emission spectroscopy was applied to determine the vibrational‐state dependence. The roaming signature was verified theoretically by quasi‐classical trajectory calculations. As an alternative, a multi‐center impulsive model was developed to simulate the roaming scalar and vector properties without involving the global energy surface.

Spectroscopic Studies of Synthetic and Natural Saponites: A Review

Saponite is a trioctahedral 2:1 smectite with the ideal composition MxMg3AlxSi4−xO10(OH,F)2.nH2O (M = interlayer cation). Both the success of the saponite synthesis and the determination of its applications depends on robust knowledge of the structure and composition of saponite. Among the routine characterization techniques, spectroscopic methods are the most common. This review, thus, provides an overview of various spectroscopic methods to characterize natural and synthetic saponites with focus on the extensive work by one of the authors (JTK). The Infrared (IR) and Raman spectra of natural and synthetic saponites are discussed in detail including the assignment of the observed bands. The crystallization of saponite is discussed based on the changes in the IR and Raman spectra and a possible crystallization model is provided. Infrared emission spectroscopy has been used to study the thermal changes of saponite in situ including the dehydration and (partial) dehydroxylation up to 750 °C. 27Al and 29Si magic-angle-spinning nuclear magnetic resonance spectroscopy is discussed (as well as 11B and 71Ga for B- and Ga-Si substitution) with respect to, in particular, Al(IV)/Al(VI) and Si/Al(IV) ratios. X-ray photoelectron spectroscopy provides chemical information as well as some information related to the local environments of the different elements in the saponite structure as reflected by their binding energies.

Time-resolved Fourier transform infrared emission spectroscopy of CO ∆v = 1 and ∆v = 2 extended bands in the ground X1Σ+ state produced by formamide glow discharge

This paper presents an extension to our knowledge of ∆v = 1 and ∆v = 2 bands of carbon monoxide in the ground state, measured by Fourier transform infrared spectroscopy of glow discharge of formamide-nitrogen mixture. Lines in declared bands are measured up to v = 30 for ∆v = 1 and up to v = 24 for ∆v = 2 band, by use of both InSb and MCT detectors, which have not been measured in the laboratory before. Dunham parameters obtained by fitting our lines are presented as well as comparison to other authors. The paper also demonstrates the interesting impossibility of sufficient population of ∆v = 2 band of CO when only pure CO is used in the glow discharge, instead of formamide-based mixture. Additionally, we present a non-LTE model to describe the intensity pattern of the ∆v = 1 and the ∆v = 2 bands of 12C16O experimental spectra by simulating the corresponding non-LTE vibrational populations of CO.

Non-Planckian infrared emission from GaAs devices with electrons and lattice out-of-thermal-equilibrium

With the downscaled device size, electrons in semiconductor electronics are often electrically driven out-of-thermal-equilibrium with hosting lattices for their functionalities. The thereby electrothermal Joule heating to the lattices can be visualized directly by the noncontact infrared radiation thermometry with the hypothetic Planck distribution at a single characteristic temperature. We report here that the infrared emission spectrum from electrically biased GaAs devices deviates obviously from Planck distribution, due to the additional contribution from non-equilibrium hot electrons whose effective temperature reaches much higher than that of the lattice (Te>Tl). The evanescent infrared emission from these hot electrons is out-coupled by a near-field metamaterial grating and is hence made significant to the total far-field emission spectrum. Resonant emission peak has also been observed when the electron hotspots are managed to overlap spatially with the optical hotspots at the grating resonance. Our work opens a new direction to study nonequilibrium dynamics with (non-Planckian) infrared emission spectroscopy and provides important implications into the microscopic energy dissipation and heat management in nanoelectronics.

Analysis of Emission Infrared Spectra of Protein Solutions in Low Concentrations

In this work, based on the method of infrared emission spectroscopy, the study of emission spectra of interferon-gamma (IFNγ) solution in a mixture or surrounded by three low-concentration solutions (IFNγ, antibodies to IFNγ, glycine buffer) or water control was performed. First of all, the solutions of low concentrations themselves were studied. It was shown that low-concentration solutions of IFNγ and antibodies to IFNγ had lower emission intensity in three spectral bands near 800, 1,300 and 2000 cm−1 compared to water control. Glycine buffer solution had a radiation level indistinguishable from that of the control. In this work, the effect of adding these low-concentration solutions to IFNγ (1 mg/ml) was compared to the effect of adding water control to IFNγ. All solutions or water were added in 10% (v/v). It was found that adding each of the three test solutions induced an increase in the radiation intensity of the IFNγ solution in the spectral range of 400–1700 cm−1 (compared to the IFNγ solution with control spike). It was also tested whether the radiation of the studied low-concentration solutions surrounding the IFNγ solution (1 mg/ml) affected the IFNγ radiation. The measurement results were compared to the data obtained for IFNγ surrounded by water control. All three solutions were found to exert a distant effect on the IFNγ solution (1 mg/ml), which was manifested in a decrease in the intensity of its radiation near 1,000 and 1,500 cm−1 compared to the control solution of IFNγ. Thus, the emission spectra of low-concentration aqueous solutions were measured for the first time, and differences in the emission spectra of the IFNγ solution depending on low-concentration additives and the environment were shown. The paper interprets the observed differences and discusses possible mechanisms underlying the observed phenomena.

Microwave-assisted modulation of light emission intensity in alkali-pyrotechnic plumes

Creating next-generation pyrotechnic emitters capable of dynamically controllable light output requires a paradigm shift away from emission control via formulation. This work demonstrates the ability to modulate light emission intensity of a pyrotechnic flame with 2.46 GHz microwave energy within a multimodal cavity. Stoichiometric mixtures of three pyrotechnic systems are investigated: magnesium fuel with oxidizers of NaNO3, KNO3, or CsNO3. Using time-resolved visible and infrared emission spectroscopy and high-speed color videography, microwave illumination of flames is found to produce enhanced atomic photo emission from the alkali species. Emission increases of up to ~120% are demonstrated, which are predominantly in the visible and near-infrared wavelengths and have little effect on flame emission chromaticity. At near- and mid-IR wavelengths, gray body continuum enhancement is observed with moderate enhanced emission from CO2 and H2O bands. Sustained light emission from microwave illumination of combustion products long after pyrotechnic extinguishment was also demonstrated. A simplified model of microwave-enhanced visible and near-IR emission is presented and shown to be consistent with the observed trend of elevated emission enhancement for lower wavelength alkali transitions. Sensitivity analysis is performed which suggests a lower equilibrium population of electronically excited alkali atoms is primarily responsible for maximizing the degree of light emission enhancement of applied microwave fields, especially in extinguished low-temperature pyrotechnic plumes. These findings suggest microwave illumination of alkali-containing pyrotechnic flames may be a useful strategy to achieve dynamic control of light emission intensity.

Roaming Dynamics and Conformational Memory in Photolysis of Formic Acid at 193\u2009nm Using Time-resolved Fourier-transform Infrared Emission Spectroscopy

In photodissociation of trans-formic acid (HCOOH) at 193 nm, we have observed two molecular channels of CO + H2O and CO2 + H2 by using 1 μs-resolved Fourier-transform infrared emission spectroscopy. With the aid of spectral simulation, the CO spectra are rotationally resolved for each vibrational state (v = 1–8). Each of the resulting vibrational and rotational population distributions is characteristic of two Boltzmann profiles with different temperatures, originating from either transition state pathway or OH-roaming to form the same CO + H2O products. The H2O roaming co-product is also spectrally simulated to understand the interplay with the CO product in the internal energy partitioning. Accordingly, this work has evaluated the internal energy disposal for the CO and H2O roaming products; especially the vibrational-state dependence of the roaming signature is reported for the first time. Further, given a 1 μs resolution, the temporal dependence of the CO/CO2 product ratio at v ≥ 1 rises from 3 to 10 of study, thereby characterizing the effect of conformational memory and well reconciling with the disputed results reported previously between absorption and emission methods.