Two species-one wavelength detection based on selective optical saturation spectroscopy.

Cross-sensitivity limits accurate quantitative detection of species concentrations in all sensor technologies, including laser-based absorption techniques. Absorption sensors capture a signal that combines contributions from all interfering species at a given detection wavelength. Careful selection of the probed spectral line, broadband detection, or upstream separation can partially mitigate cross-sensitivity, however, weak or unidentified signal interference remains a challenge for accuracy.

Systematic Study on Zirconium Chelidamates: From a Molecular Complex to a M-HOF and a MOF.

We report the synthesis and in-depth characterization of three zirconium chelidamates, a molecular complex (HCN)[Zr(HL)] (), a porous metal-containing hydrogen-bonded organic framework (M-HOF) [Zr(HO)(HL)]·HO (), and a metal-organic framework (MOF) (HCN)[Zr(HL)]· solvent (0 ≤ ≤ 1) () using chelidamic acid (HL, HCNO, 4-hydroxypyridine-2,6-dicarboxylic acid) as the ligand (HCN = dimethylammonium). High-throughput investigations of the system Zr/HL/HCl/DMF/HO were carried out, which resulted in highly crystalline compounds. The crystal structures of and were determined by single-crystal X-ray diffraction.

Plastiglomerates from uncontrolled burning of plastic waste on Indonesian beaches contain high contents of organic pollutants.

This study reports on plastiglomerate and other new forms of plastic pollution in the tropical marine continent of Indonesia. Twenty-five samples were collected from an island beach in the Java Sea where plastiglomerate, plasticrusts, and pyroplastic were formed by the uncontrolled burning of plastic waste. The most common plastic types were polyethylene and polypropylene (PE/PP), as shown by ATR-FTIR spectroscopy.

Mid-infrared Frequency Modulation Detection of HCN and Its Reaction with O Atoms behind Shock Waves.

Hydrogen cyanide (HCN) is the primary cyanide species in combustion processes and plays a key role in the formation of NO in the combustion of fossil fuels, nitrogen-containing biofuels, and blended hydrocarbon-ammonia mixtures. Robust, sensitive, and time-resolved in situ laser diagnostic methods are needed to gain insight into the combustion chemistry of HCN. Mid-infrared frequency modulation spectroscopy (MIR-FMS) has recently been established as such a quantitative technique for HCN detection behind shock waves.

Ab Initio and RRKM/Master Equation Analysis of the Photolysis and Thermal Unimolecular Decomposition of Bromoacetaldehyde.

Bromoacetaldehyde (BrCHCHO) is a major stable brominated organic intermediate of the bromine-ethylene addition reaction during the arctic bromine explosion events. Similar to acetaldehyde, which has been recently identified as a source of organic acids in the troposphere, it may be subjected to photo-tautomerization initially forming brominated vinyl compounds. In this study, we investigate the unimolecular reactions of BrCHCHO under both photolytic and thermal conditions using high-level quantum chemical calculations and Rice-Ramsperger-Kassel-Marcus (RRKM)/master equation analysis.

Kinetics of 1- and 2-methylallyl + O reaction, investigated by photoionisation using synchrotron radiation.

The reaction kinetics of the isomers of the methylallyl radical with molecular oxygen has been studied in a flow tube reactor at the vacuum ultraviolet (VUV) beamline of the Swiss Light Source storage ring. The radicals were generated by direct photodissociation of bromides or iodides at 213 nm. Experiments were conducted at room temperature and low pressures between 1 and 3 mbar using He as the buffer gas.

The Reaction NCN + H: Quantum Chemical Calculations, Role of NCN Chemistry, and NCN Absorption Cross Section.

The NCN radical plays a key role for modeling prompt-NO formation in hydrocarbon flames. Recently, in a combined shock tube and flame modeling study, the so far neglected reaction NCN + H and the related chemistry of the main product HNCN turned out to be significant for NO modeling under fuel-rich conditions. In this study, the reaction has been thoroughly revisited by detailed quantum chemical rate constant calculations both for the singlet NCN and triplet NCN pathways.

Single-tone mid-infrared frequency modulation spectroscopy for sensitive detection of transient species.

A single-tone mid-infrared frequency modulation (MIR-FM) spectrometer consisting of a cw-OPO-based laser system, a 500 MHz LiTaO electro-optical modulator (EOM), and a high-bandwidth GaAs mid-infrared detector has been developed. In order to assess the instrument's sensitivity and time resolution, FM spectra of selected CH transitions around 3070 cm were measured and the reaction Cl + CH following the 193 nm excimer laser photolysis of oxalyl chloride was investigated by recording concentration-time profiles of HCl at 2925.90 cm in a low-pressure slow-flow reactor.

The first water-based synthesis of Ce(iv)-MOFs with saturated chiral and achiral C-dicarboxylate linkers.

Six different chiral and achiral alkane dicarboxylic C-acids, i.e. succinic acid (HSUC), dl-2-methylsuccinic acid (HMS), 2,3-dimethylsuccinic acid (HDMS) and aspartic acid (d-, l- and dl-HASP), were used to obtain Ce(iv)-MOFs via microwave assisted reactions.

Kinetics in the real world: linking molecules, processes, and systems.

Unravelling elementary steps, reaction pathways, and kinetic mechanisms is key to understanding the behaviour of many real-world chemical systems that span from the troposphere or even interstellar media to engines and process reactors. Recent work in chemical kinetics provides detailed information on the reactive changes occurring in chemical systems, often on the atomic or molecular scale. The optimisation of practical processes, for instance in combustion, catalysis, battery technology, polymerisation, and nanoparticle production, can profit from a sound knowledge of the underlying fundamental chemical kinetics.

Quantitative Mid-Infrared Cavity Ringdown Detection of Methyl Iodide for Monitoring Applications.

Methyl iodide is a toxic halocarbon with diverse industrial and agricultural applications, and it is an important ocean-derived trace gas that contributes to the iodine burden of the atmosphere. Quantitative analysis of CHI is mostly based on gas chromatography coupled with mass spectrometry or electron capture detection (GC-MS/ECD) as of yet, which often limits the ability to conduct in situ high-frequency monitoring studies. This work presents an alternative detection scheme based on mid-infrared continuous wave cavity ringdown spectroscopy (mid-IR cw-CRDS).

Doppler-limited high-resolution spectrum and VPT2 assisted assignment of the C-H stretch of CHBr.

The Doppler limited non-saturated rotationally resolved infrared spectra of the symmetric and asymmetric CH-stretch bands of CHBr have been measured. A continuous wave cavity ringdown setup with a widely tunable Mid-IR-OPO laser light source yielded a single-shot minimum absorption of 4.9×10cm.

Saturation dynamics and working limits of saturated absorption cavity ringdown spectroscopy.

Cavity ringdown spectroscopy (CRDS) in the linear absorption regime is a well-established method for sensitive trace gas detection, but only a few studies have addressed quantitative measurements in the presence of a saturated sample. In fact, saturation is usually avoided in order to escape from the required complex modeling of the saturation process that depends on the characteristics of the absorbing species, its interaction with the surrounding gas as well as on the temporal and spectral characteristics of the cavity excitation. Conversely, the novel saturated-absorption cavity ringdown spectroscopy approach (SCAR/Sat-CRDS) takes advantage of sample saturation in order to allow one to extract both the gas absorption and the empty cavity loss rates from a single ringdown event.

The rate constant of the reaction NCN + H2 and its role in NCN and NO modeling in low pressure CH4/O2/N2-flames.

Bimolecular reactions of the NCN radical play a key role in modeling prompt-NO formation in hydrocarbon flames. The rate constant of the so-far neglected reaction NCN + H2 has been experimentally determined behind shock waves under pseudo-first order conditions with H2 as the excess component. NCN3 thermal decomposition has been used as a quantitative high temperature source of NCN radicals, which have been sensitively detected by difference UV laser absorption spectroscopy at [small nu, Greek, tilde] = 30383.

Glyoxal Oxidation Mechanism: Implications for the Reactions HCO + O2 and OCHCHO + HO2.

A detailed mechanism for the thermal decomposition and oxidation of the flame intermediate glyoxal (OCHCHO) has been assembled from available theoretical and experimental literature data. The modeling capabilities of this extensive mechanism have been tested by simulating experimental HCO profiles measured at intermediate and high temperatures in previous glyoxal photolysis and pyrolysis studies. Additionally, new experiments on glyoxal pyrolysis and oxidation have been performed with glyoxal and glyoxal/oxygen mixtures in Ar behind shock waves at temperatures of 1285-1760 K at two different total density ranges.

Direct measurements of the total rate constant of the reaction NCN + H and implications for the product branching ratio and the enthalpy of formation of NCN.

The overall rate constant of the reaction (2), NCN + H, which plays a key role in prompt-NO formation in flames, has been directly measured at temperatures 962 K < T < 2425 K behind shock waves. NCN radicals and H atoms were generated by the thermal decomposition of NCN3 and C2H5I, respectively. NCN concentration-time profiles were measured by sensitive narrow-line-width laser absorption at a wavelength of λ = 329.

Bismuth tri- and tetraarylcarboxylates: crystal structures, in situ X-ray diffraction, intermediates and luminescence.

A systematic investigation of the systems Bi(3+)/carboxylic acid/HNO3 for the tri- and tetracarboxylic acids pyromellitic acid (H4Pyr), trimellitic acid (H3Tri) and trimesic acid (H3BTC) acid led to the discovery of five new bismuth carboxylates. Structural characterisation allowed the influence of the linker geometry and the Bi(3+):linker molar ratio in the starting solution on the crystal structure to be determined. The crystallisation of three selected compounds was investigated by in situ energy-dispersive X-ray diffraction.

Quantitative time-resolved vibrational sum frequency generation spectroscopy as a tool for thin film kinetic studies: new insights into oleic acid monolayer oxidation.

Environmental air-water interfaces are often covered by thin films of surface-active organic substances that play an important role for air-sea gas exchange and aerosol aging. Surface-sensitive vibrational sum frequency generation (VSFG) spectroscopy has been widely used to study the static structure of organic monolayers serving as simple model systems of such films. Probably due to the difficulties to correlate the SFG signal intensity with the surface concentration, corresponding time-resolved studies of surface reactions are scarce.

Design and field application of a UV-LED based optical fiber biofilm sensor.

Detecting changes in the formation dynamics of biofilms stemming from bacteria and unicellular microorganisms in their natural environment is of prime interest for biological, ecological as well as anti-fouling technology research. We developed a robust optical fiber-based biofilm sensor ready to be applied in natural aquatic environments for on-line, in situ and non-destructive monitoring of large-area biofilms. The device is based on the detection of the natural fluorescence of microorganisms constituting the biofilm.

Dimerization of HNO in aqueous solution: an interplay of solvation effects, fast acid-base equilibria, and intramolecular hydrogen bonding?

The recent unraveling of the rather complex acid-base equilibrium of nitroxyl (HNO) has stimulated a renewed interest in the significance of HNO for biology and pharmacy. HNO plays an important role in enzymatic mechanisms and is discussed as a potential therapeutic agent against heart failure. A cumbersome property for studying HNO reactions, its fast dimerization leading to the rapid formation of N(2)O, is surprisingly far from being well understood.

Direct measurements of the high temperature rate constants of the reactions NCN + O, NCN + NCN, and NCN + M.

The rate constant of the reaction NCN + O has been directly measured for the first time. According to the revised Fenimore mechanism, which is initiated by the NCN forming reaction CH + N(2)→ NCN + H, this reaction plays a key role for prompt NO(x) formation in flames. NCN radicals and O atoms have been quantitatively generated by the pyrolysis of NCN(3) and N(2)O, respectively.

A precise high-resolution near infrared continuous wave cavity ringdown spectrometer using a Fourier transform based wavelength calibration.

A wavelength calibration technique is described, which is based on a combination of a Fourier transform wavelength meter and a distributed feedback laser locked to a molecular transition as a frequency marker in the spectrum. The technique provides a reliable wavelength scale to be used in high resolution continuous wave cavity ringdown spectroscopy without need for stabilization of the probe laser and accurately known molecular transitions in the scanned wavelength range. Due to a continuous reference measurement, ambient influences on the laser sources are effectively suppressed.

HCO formation in the thermal unimolecular decomposition of glyoxal: rotational and weak collision effects.

The multi-channel thermal unimolecular decomposition of glyoxal was experimentally investigated in the temperature range 1106 K < T < 2320 K and at total densities of 1.7 x 10(-6) mol cm(-3) < rho < 1.9 x 10(-5) mol cm(-3) by monitoring HCO (frequency modulation spectroscopy, FMS), (CHO)(2) (UV absorption), and H atom (atom resonance absorption spectroscopy, H-ARAS) concentration-time profiles behind shock waves.

C-H bond activation of coordinated pyridine: ortho-pyridyl-ditechnetiumhydridocarbonyl metal cyclus. Crystal structure and dynamic behavior in solution.

The reaction of pyridine with ditechnetium decacarbonyl [Tc2(CO)10] (1) leads to a novel ortho-pyridyl-ditechnetium hydrido complex, [Tc2(mu-H)(mu-NC5H4)(NC5H5)2(CO)6] (2) and its precursor [Tc2(mu-CO)2(NC5H5)2(CO)6] (3). At ambient temperature 1 was found to react slowly with pyridine to afford the substitution product 3 after 120 h. However, heating the reaction mixture to reflux exclusively leads to the pyridine-ortho-metalated complex 2 in only 30 min.

Time-resolved cavity ringdown measurements and kinetic modeling of the pressure dependences of the recombination reactions of SiH2 with the alkenes C2H4, C3H6, and t-C4H8.

Room-temperature rate constants for the pressure-dependent reactions SiH2 + ethene, propene, and t-butene have been determined at total pressures of 3.3 mbar < or = p < or = 300 mbar with Ar as buffer gas. SiH2 was detected by means of time-resolved cavity ringdown spectroscopy (CRDS), and the deconvolution of ringdown, kinetics, and laser bandwidth effect was accomplished with the extended simultaneous kinetics and ringdown model (eSKaR).