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Seagrass meadows are autotrophic ecosystems acting as carbon sinks, but they have also been shown to be sources of carbon dioxide (CO2) and methane (CH4). Seagrasses can be negatively affected by increasing seawater temperatures, but the effects of warming on CO2 and CH4 fluxes in seagrass meadows have not yet been reported. Here, we examine the effect of two disturbances on air–seawater fluxes of CO2 and CH4 in Red Sea Halophila stipulacea communities compared to adjacent unvegetated sediments using cavity ring-down spectroscopy. We first characterized CO2 and CH4 fluxes in vegetated and adjacent unvegetated sediments, and then experimentally examined their response, along with that of the carbon (C) isotopic signature of CO2 and CH4 , to gradual warming from 25 ∘ C (winter seawater temperature) to 37 ∘ C, 2 ∘ C above current maximum temperature. In addition, we assessed the response to prolonged darkness, thereby providing insights into the possible role of suppressing plant photosynthesis in supporting CO2 and CH4 fluxes. We detected 6-fold-higher CO2 fluxes in vegetated compared to bare sediments, as well as 10- to 100-fold-higher CH4 fluxes. Warming led to an increase in net CO2 and CH4 fluxes, reaching average fluxes of 10 422.18 ± 2570.12 µ mol CO2 m -2 d -1 and 88.11±15.19 µ mol CH4 m -2 d -1 , while CO2 and CH4 fluxes decreased over time in sediments maintained at 25 ∘ C. Prolonged darkness led to an increase in CO2 fluxes but a decrease in CH4 fluxes in vegetated sediments. These results add to previous research identifying Red Sea seagrass meadows as a significant source of CH4 , while also indicating that sublethal warming may lead to increased emissions of greenhouse gases from seagrass meadows, providing a feedback mechanism that may contribute to further enhancing global warming. [ABSTRACT FROM AUTHOR]

Oxygen is the dominant element in our planetary system. It is therefore remarkable that it shows substantial isotopic diversity both in mass-dependent fractionation, because it is a light element, and in mass-independent fractionation, primarily associated with variation in abundance of 16O. On Earth, the primary variation in isotopic composition is related to temperature-dependent kinetic mass fractionation between hydrosphere and atmosphere. Meteorites provide samples of primitive bodies, that have not experienced melting, and planetesimals that have melted early in their history. Samples of Mars, Vesta, and the Moon are present in the meteorite collections. In meteorites, the cosmochemical fractionation related to the abundance of 16O provides a useful classification scheme. Inclusions in chondrites show a large range in 16O abundances from highly enriched (solar) through to compositions closer to terrestrial (planetary). The variability in 16O appears originally to be related to predissociation and self-shielding of carbon monoxide likely in the primordial molecular cloud. Within the chondrite parent bodies, exchange between 16O-poor fluids and relatively 16O-rich solids created isotopic mixing lines. This model makes specific predictions for isotopic compositions of silicates and water ice throughout the solar system. One prediction, that the Earth should be isotopically heavier than the Sun, appears to be verified. But other tests based on oxygen isotopes within the solar system require either remote analysis or sample return missions. Remote analysis will require new instrumentation and analytical techniques to achieve the precision and accuracy required for three oxygen isotope analysis. Methodologies associated with cavity ring-down spectroscopy appear promising. Sample return appears viable only for the inner solar system including Mars and asteroids. While sample return missions to either Venus or Mercury appear highly challenging, the scientific benefits are immense both in oxygen isotope characterisation, and in a variety of other geochemical analyses. Measurement of three oxygen isotopes throughout the solar system would further our concepts for formation of other solar systems, and give us insight into the general mechanisms of planetary system formation and the role of water in the formation and evolution of the chondrite parent bodies and planets. [ABSTRACT FROM AUTHOR]

The rate constants of the reactions of DO2 + HO2 (R1) and DO2 + DO2 (R2) have been determined by the simultaneous, selective, and quantitative measurement of HO2 and DO2 by continuous wave cavity ring‐down spectroscopy (cw‐CRDS) in the near infrared, coupled to a radical generation by laser photolysis. HO2 was generated by photolyzing Cl2 in the presence of CH3OH and O2. Low concentrations of DO2 were generated simultaneously by adding low concentrations of D2O to the reaction mixture, leading through isotopic exchange on tubing and reactor walls to formation of low concentrations of CH3OD and thus formation of DO2. Excess DO2 was generated by photolyzing Cl2 in the presence of CD3OD and O2, small concentrations of HO2 were always generated simultaneously by isotopic exchange between CD3OD and residual H2O. The rate constant k1 at 295 K was found to be pressure independent in the range 25–200 Torr helium, but increased with increasing D2O concentration k1 = (1.67 ± 0.03) × 10−12 × (1 + (8.2 ± 1.6) × 10−18 cm3 × [D2O] cm−3) cm3 s−1. The rate constant for the DO2 self‐reaction k2 has been measured under excess DO2 concentration, and the DO2 concentration has been determined by fitting the HO2 decays, now governed by their reaction with DO2, to the rate constant k1. A rate constant with insignificant pressure dependence was found: k2 = (4.1 ± 0.6) × 10−13 (1 + (2 ± 2) × 10−20 cm3 × [He] cm−3) cm3 s−1 as well as an increase of k2 with increasing D2O concentration was observed: k2 = (4.14 ± 0.02) × 10−13 × (1 + (6.5 ± 1.3) × 10−18 cm3 × [D2O] cm−3) cm3 s−1. The result for k2 is in excellent agreement with literature values, whereas this is the first determination of k1. [ABSTRACT FROM AUTHOR]

The rate constants of the reactions of DO2 + HO2 (R1) and DO2 + DO2 (R2) have been determined by the simultaneous, selective, and quantitative measurement of HO2 and DO2 by continuous wave cavity ring‐down spectroscopy (cw‐CRDS) in the near infrared, coupled to a radical generation by laser photolysis. HO2 was generated by photolyzing Cl2 in the presence of CH3OH and O2. Low concentrations of DO2 were generated simultaneously by adding low concentrations of D2O to the reaction mixture, leading through isotopic exchange on tubing and reactor walls to formation of low concentrations of CH3OD and thus formation of DO2. Excess DO2 was generated by photolyzing Cl2 in the presence of CD3OD and O2, small concentrations of HO2 were always generated simultaneously by isotopic exchange between CD3OD and residual H2O. The rate constant k1 at 295 K was found to be pressure independent in the range 25–200 Torr helium, but increased with increasing D2O concentration k1 = (1.67 ± 0.03) × 10−12 × (1 + (8.2 ± 1.6) × 10−18 cm3 × [D2O] cm−3) cm3 s−1. The rate constant for the DO2 self‐reaction k2 has been measured under excess DO2 concentration, and the DO2 concentration has been determined by fitting the HO2 decays, now governed by their reaction with DO2, to the rate constant k1. A rate constant with insignificant pressure dependence was found: k2 = (4.1 ± 0.6) × 10−13 (1 + (2 ± 2) × 10−20 cm3 × [He] cm−3) cm3 s−1 as well as an increase of k2 with increasing D2O concentration was observed: k2 = (4.14 ± 0.02) × 10−13 × (1 + (6.5 ± 1.3) × 10−18 cm3 × [D2O] cm−3) cm3 s−1. The result for k2 is in excellent agreement with literature values, whereas this is the first determination of k1. [ABSTRACT FROM AUTHOR]

A kinetic study of the reaction of the 4‐methylphenyl radical (4‐C6H4CH3) with the oxygen molecule was conducted using experimental and theoretical approaches. The absorption spectrum for the λ = 266 nm photolysis of the 4‐C6H4CH3X (X = Cl, Br)/N2/O2 mixture was measured in the wavelength range of λ = 503‐512 nm using N2 as the buffer gas at a total pressure of 40 Torr using a cavity ring‐down spectroscopy apparatus coupled with a pulsed laser photolysis system. Based on the absorbance of the product of the 4‐C6H4CH3 + O2 reaction at λ = 504 nm, the reaction rate coefficient for the 4‐C6H4CH3 + O2 reaction was determined to be k = (1.21 ± 0.10) × 10−11 cm3 molecule−1 s−1 and k = (1.18 ± 0.21) × 10−11 cm3 molecule−1 s−1 using 4‐C6H4CH3Cl and 4‐C6H4CH3Br, respectively, as the radical precursor. And there was no pressure dependence in the total pressure range of 10‐90 Torr varying partial pressure of N2 buffer gas at T = 296 ± 5 K. The geometries, vibration frequencies, and potential energy surfaces of the reactants, major products, and transition states in the 4‐C6H4CH3 + O2 reaction were determined using the CBS‐QB3 method. The k value at the high‐pressure limit was calculated to be 1.26 × 10−11 cm3 molecule−1 s−1 using the variational transition‐state theory. The calculated value of k was consistent with the experimental value, which indicated that the 4‐C6H4CH3 + O2 reaction reaches the high‐pressure limit at 10 Torr. Therefore, the oxidation of the 4‐C6H4CH3 radical is almost 10 times faster than that of the benzyl radical, which has the same chemical formula, at the high‐pressure limit. [ABSTRACT FROM AUTHOR]

NO3 and N2O5 are important participants in nocturnal atmospheric chemical processes, and their concentrations are of great significance in the study of the mechanism of nocturnal atmospheric chemical reactions. A two-channel diode laser based cavity ring-down spectroscopy (CRDS) instrument was developed to monitor the concentrations of NO3 and N2O5 in the atmosphere. The effective absorption length ratio and the total loss coefficient of the instrument were calibrated using laboratory standard samples. The effective absorption cross section of NO3 at 662 nm was derived. A detection sensitivity of 1.1 pptv NO3 in air was obtained at a time resolution of 1 s. N2O5was converted to NO3 and detected online in the second CRDS channel. The instrument was used to monitor the concentrations of NO3 and N2O5 in the atmosphere of winter in Hefei in real time. By comparing the concentration changes of pollutants such as nitrogen oxides, ozone, PM2.5 in a rapid air cleaning process, the factors affecting the concentrations of NO3 and N2O5 in the atmosphere were discussed. [ABSTRACT FROM AUTHOR]

We present the development, integration, and testing of an open-path cavity ring-down spectroscopy (CRDS) methane sensor for deployment on small unmanned aerial systems (sUAS). The open-path configuration used here (without pump or flow-cell) enables a low mass (4 kg) and low power (12 W) instrument that can be readily integrated to sUAS, defined here as having all-up mass of <25 kg. The instrument uses a compact telecom style laser at 1651 nm (near-infrared) and a linear 2-mirror high-finesse cavity. We show test results of flying the sensor on a DJI Matrice 600 hexacopter sUAS. The high sensitivity of the CRDS method allows sensitive methane detection with a precision of ~10–30 ppb demonstrated for actual flight conditions. A controlled release setup, where known mass flows are delivered, was used to simulate point-source methane emissions. Examples of methane plume detection from flight tests suggest that isolated plumes from sources with a mass flow as low as ~0.005 g/s can be detected. The sUAS sensor should have utility for emissions monitoring and quantification from natural gas infrastructure. To the best of our knowledge, it is also the first CRDS sensor directly deployed onboard an sUAS. [ABSTRACT FROM AUTHOR]

The large RF negative hydrogen (deuterium) ion source at the ELISE test facility (half of the ITER-NBI source size) has been equipped with a Cavity Ring-Down Spectroscopy (CRDS) system, in order to measure the negative hydrogen (deuterium) ion density in the region in front of the plasma grid (first grid of the extraction system). The challenge of this diagnostic for ELISE relies on the large size of the source and therefore on the plasma length across which the measurements are performed as well as the long pulses at RF power, which can affect the cavity mirror reliability. A dedicated experiment on the mirror reliability was performed, ensuring the feasibility of measurements for long pulses (several hundred seconds) at high RF power. Two horizontal lines of sight were dedicated to CRDS: the measured density was in the range between 4 × 1016 and 1 × 1017 m−3, with a slightly higher density for the bottom lines of sight, for both the isotope hydrogen and deuterium. Different temporal evolution was observed for the two isotopes, showing a higher instability for the deuterium case: this is in correlation with the extracted negative ion current density and inversely correlated with the coextracted electron current density. The CRDS system allowed performing the first measurements of negative ion density for a long pulse (1000 s) in a large source: the temporal behavior and the effect of the beam extraction will also be discussed. [ABSTRACT FROM AUTHOR]

Atmospheric trace gas measurements of greenhouse gases are critical in their precision and accuracy. In the past 5 years, atmospheric measurement and gas metrology communities have turned their attention to possible surface effects due to pressure and temperature variations during a standard cylinder's lifetime. This study concentrates on this issue by introducing newly built small-volume aluminum and steel cylinders which enable the investigation of trace gases and their affinity for adsorption and desorption on various surfaces over a set of temperature and pressure ranges. The presented experiments are designed to test the filling pressure dependencies up to 30 bar and temperature dependencies from -10 ∘ C up to 180 ∘ C for these prototype cylinders. We present measurements of CO2 , CH4 , CO and H2O using a cavity ring-down spectroscopy analyzer under these conditions. Moreover, we investigated CO2 amount fractions using a novel quantum cascade laser spectrometer system enabling measurements at pressures as a low as 5 mbar. This extensive dataset revealed that for absolute pressures down to 150 mbar the enhancement in the amount fraction of CO2 relative to its initial value (at 1200 mbar absolute) is limited to 0.12 µ mol mol -1 for the prototype aluminum cylinder. Up to 80 ∘ C, the aluminum cylinder showed superior results and less response to varying temperature compared to the steel cylinder. For CO2 , these changes were insignificant at 80 ∘ C for the aluminum cylinder, whereas a 0.11 µ mol mol -1 enhancement for the steel cylinder was observed. High-temperature experiments showed that for both cylinders irreversible temperature effects occur especially above 130 ∘ C. [ABSTRACT FROM AUTHOR]

This work describes an incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) instrument for quantification of HONO and NO2 mixing ratios in ambient air. The instrument is operated in the near-ultraviolet spectral region between 361 and 388 nm. The mirror reflectivity and optical cavity transmission function were determined from the optical extinction observed when sampling air and helium. To verify the accuracy of this approach, Rayleigh scattering cross sections of nitrogen and argon were measured and found to be in quantitative agreement with literature values. The mirror reflectivity exceeded 99.98 %, at its maximum near 373 nm, resulting in an absorption path length of 6 km from a 1 m long optical cavity. The instrument precision was assessed through Allan variance analyses and showed minimum deviations of ±58 and ±210 pptv (1σ) for HONO and NO2 , respectively, at an optimum acquisition time of 5 min. Measurements of HONO and NO2 mixing ratios in laboratory-generated mixtures by IBBCEAS were compared to thermal dissociation cavity ring-down spectroscopy (TD-CRDS) data and agreed within combined experimental uncertainties. Sample ambient air data collected in Calgary are presented. [ABSTRACT FROM AUTHOR]

A critical issue for the long-term monitoring of atmospheric trace gases is precision and accuracy of the measurement systems employed. Both measuring and preparing reference gas mixtures for trace gases are challenging due to, for example, adsorption and desorption of the substances of interest on surfaces; this is particularly critical at low amount fractions and/or for reactive gases. Therefore, to ensure the best preparation and measurement conditions for trace gases in very low amount fractions, usage of coated materials is in demand in gas metrology and atmospheric measurement communities. This study focuses on testing potential adsorption and desorption effects for different materials or coatings that are currently used or that may be relevant in the future for the measurements of greenhouse gases. For this study we used small volume chambers designed to be used for adsorption studies. Various materials with or without coatings were loaded into the small cylinder to test their adsorption and desorption behavior. We used the aluminum cylinder as the measurement chamber and glass, aluminum, copper, brass, steel and three different commercially available coatings as test materials. Inserting the test materials into the measurement chamber doubles the available geometric area for the surface processes. The presented experiments were designed to investigate the pressure dependency of adsorption up to 15 bar and its temperature dependency up to 80 ∘ C for the test materials placed in the measurement chamber. Here, we focused on the species CO2 , CH4 , CO and H2O measured by a cavity ring-down spectroscopy analyzer. Our results show that the materials currently used in atmospheric measurements are well suited. The investigated coatings were not superior to untreated aluminum or to stainless steel at the tested pressure ranges, whereas under changing temperature aluminum showed better performance for CO2 (<0.05 µ mol mol -1 change in measured amount fractions) than stainless steel (>0.1 µ mol mol -1). To our knowledge, this study is one of the first attempts to investigate surface effects of different materials in such a setup for the abovementioned gases. [ABSTRACT FROM AUTHOR]

The ultimate sensitivity performances obtained with a continuous wave-cavity ring down spectroscopy setup in the near infrared are investigated. At fixed frequency, the noise of the photodetector is found to be the main limitation and the best limit of detection (about 10-11 cm-1) is reached after a 10 s averaging. We show that long term baseline fluctuations can be efficiently averaged over several days allowing us to reach a detection limit as low as 5 × 10-13 cm-1. The achieved sensitivity is illustrated on narrow spectral intervals where the weakest lines detected so far by absorption spectroscopy are observed: (i) ultra-weak transitions of the a1Δg(0)-X 3Σg-(1) hot band of 16O2 near 1.58 μm and (ii) first detection of an electric quadrupole transition in the second overtone band of nitrogen (14N2) near 1.44 μm. [ABSTRACT FROM AUTHOR]

We have demonstrated a spectroscopic technique for simultaneously obtaining broad spectral bandwidth and high frequency resolution absorption measurements, with 5 μs temporal resolution, continuously for tens of microseconds in an apparatus with no active stabilization. The technique utilizes two passive air-gap etalons to imprint two frequency comb patterns onto a single pulsed light source. The air-gap etalons also serve as cavity ringdown cells increasing the sensitivity of the absorption spectroscopy by increasing the interrogation path length. Here, we demonstrate the operation of the spectrometer utilizing a ∼0.15 cm-1 bandwidth pulsed dye laser and two nearly identical 300 MHz free-spectral range confocal air-gap etalons each with a finesse of ∼1 × 105, to investigate the (1,1,3) overtone of water and the R(7) transition of the O2 b1Σg+←X3Σg- (2,0) band with high spectral resolution. [ABSTRACT FROM AUTHOR]

Absolute positions of several oxygen B-band lines were measured with the Pound-Drever-Hall-locked frequency-stabilized cavity ring-down spectrometer. The frequency axis of spectra was linked to the optical frequency comb. Achieved uncertainties of line positions are between 0.9 and 2.9 MHz. Self-pressure shifts coefficients are also reported. [ABSTRACT FROM AUTHOR]

A systematic deuterium labeling experiment is presented that aims at an unambiguous determination of the geometrical ground state structure of the C9H3 and C11H3 hydrocarbon chains. Cavity ring-down spectroscopy and special plasma expansions constituting C/H, C/D, and C/H/D are used to record optical transitions of both species and their (partially) deuterated equivalents in the 19 000 cm-1 region. The number of observed bands, the quantitative determination of isotopic shifts, and supporting calculations show that the observed C9H3 and C11H3 spectra originate from HC4(CH)C4H and HC4[C(C2H)]C4H species with C2v symmetry. This result illustrates the potential of deuterium labeling as a useful approach to characterize the molecular structure of nonlinear hydrocarbon chains. [ABSTRACT FROM AUTHOR]

Frequency-stabilized cavity ring-down spectroscopy (FS-CRDS) was employed to measure air-broadened CO2 line shape parameters for transitions near 1.6 μm over a pressure range of 6.7-33 kPa. The high sensitivity of FS-CRDS allowed for the first measurements in this wavelength range of air-broadened line shape parameters on samples with CO2 mixing ratios near those of the atmosphere. The measured air-broadening parameters show several percent deviations (0.9%-2.7%) from values found in the HITRAN 2008 database. Spectra were fit with a variety of models including the Voigt, Galatry, Nelkin-Ghatak, and speed-dependent Nelkin-Ghatak line profiles. Clear evidence of line narrowing was observed, which if unaccounted for can lead to several percent biases. Furthermore, it was observed that only the speed-dependent Nelkin-Ghatak line profile was able to model the spectra to within the instrumental noise level because of the concurrent effects of collisional narrowing and speed dependence of collisional broadening and shifting. [ABSTRACT FROM AUTHOR]

Following single-photon dissociation of CH2I2 at 248 nm, I2 molecular elimination is detected by using cavity ring-down absorption spectroscopy. The technique comprises two laser beams propagating in a perpendicular configuration, in which a tunable laser beam along the axis of the ring-down cell probes the I2 fragment in the B 3Πou+ - X 1Σg+ transition. The nascent vibrational populations for v = 0, 1, and 2 levels are obtained with a population ratio of 1:(0.65 ± 0.10):(0.30 ± 0.05), corresponding to a Boltzmann-like vibrational temperature of 544 ± 73 K. The quantum yield of the ground state I2 elimination reaction is determined to be 0.0040 ± 0.0025. With the aid of ab initio potential energy calculations, the pathway of molecular elimination is proposed on the energetic ground state CH2I2 via internal conversion, followed by asynchronous three-center dissociation. A positive temperature effect supports the proposed mechanism. [ABSTRACT FROM AUTHOR]

The electric quadrupole fundamental (v=1←0) band of molecular deuterium around 3 μm is accessed by cavity ring-down spectroscopy using a difference-frequency-generation source linked to the Cs-clock primary standard via an optical frequency comb synthesizer. An absolute determination of the line position and strength is reported for the first two transitions (J=2←0 and J=3←1) of the S branch. An accuracy of 6×10-8 is achieved for the line-center frequencies, which improves by a factor 20 previous experimental results [A. R. W. McKellar and T. Oka, Can. J. Phys. 56, 1315 (1978)]. The line strength values, measured with 1% accuracy, are used to retrieve the quadrupole moment matrix elements which are found in good agreement with previous theoretical calculations [A. Birnbaum and J. D. Poll, J. Atmos. Sci. 26, 943 (1969); J. L. Hunt, J. D. Poll, and L. Wolniewicz, Can. J. Phys. 62, 1719 (1984)]. [ABSTRACT FROM AUTHOR]

This paper reports on the absorption of molecular oxygen in the region of the A-band near 760 nm under atmospheric conditions relevant for satellite retrieval studies. We use pulsed laser cavity ring-down spectroscopy with a narrow bandwidth laser and use pressure scans to increase the accuracy of the measured oxygen extinction coefficients. Absolute binary absorption coefficients in minima between absorption lines of the A-band spectrum have been measured and tabulated. We use the so-called adjustable branch coupling model including line mixing to calculate the magnetic dipole absorption in order to determine the contribution of collision induced absorption. The line mixing model has been optimized such that the collision induced absorption spectrum is smooth. [ABSTRACT FROM AUTHOR]

The hydrogen-bonded structures of pyrrole-solvent (H2O,CH3OH,C2H5OH) binary clusters were studied by the combination of experimental and theoretical techniques. Infrared cavity ringdown spectroscopy was applied to observe the NH and OH stretching vibrations of the clusters. The structures, binding energies, and normal modes of the binary clusters were obtained by quantum chemical calculations of the MP2/6-31+G(d,p) and B3LYP/6-311+G(d,p) levels. For the 1:1 clusters of pyrrole-H2O, pyrrole-CH3OH, and pyrrole-C2H5OH, the hydrogen-bonded NH stretching vibrations were observed at 3448, 3414, and 3408 cm-1, respectively. They were redshifted from the NH stretching vibration of the pyrrole monomer, and the amounts of the redshift were proportional to the proton affinities of the solvent molecules. MP2 level calculations revealed that the σ-type (NH...O) hydrogen-bonded structures had 7.6–9.0 kJ/mol larger binding energies than the π-type structures (OH...π electron cloud of pyrrole), and that the vibrational frequencies of the σ-type structures are consistent with the observed spectra. In addition to the 1:1 clusters, the NH or OH stretching vibrations of pyrrole-CH3OH binary clusters were observed at 3432 and 3549 cm-1. Among three optimized structures of the pyrrole-(CH3OH)2, the σ-π bridge pyrrole-(CH3OH)2 provided a reasonable agreement between the observed and calculated vibrational frequencies. For the pyrrole-H2O binary clusters, three new bands were observed at 3414, 3435, and 3541 cm-1. These bands are consistent with the calculated NH and OH stretching vibrations of the (pyrrole)2-H2O cluster, which has a closed cyclic hydrogen-bonded structure. [ABSTRACT FROM AUTHOR]

Absolute column densities of C2(a) and CH radicals and H(n=2) atoms have been measured in a diamond growing microwave reactor operating with hydrocarbon/Ar/H2 gas mixtures as functions of height (z) above the substrate surface and process conditions. The monitored species are each localized in the hot plasma region, where Tgas∼3000 K, and their respective column densities are each reproduced, quantitatively, by two-dimensional (r,z) modeling of the plasma chemistry. The H(n=2) distribution is seen to peak nearer the substrate, reflecting its sensitivity both to thermal chemistry (which drives the formation of ground state H atoms) and the distributions of electron density (ne) and temperature (Te). All three column densities are found to be sensitively dependent on the C/H ratio in the process gas mixture but insensitive to the particular choice of hydrocarbon (CH4 and C2H2). The excellent agreement between measured and predicted column densities for all three probed species, under all process conditions investigated, encourages confidence in the predicted number densities of other of the more abundant radical species adjacent to the growing diamond surface which, in turn, reinforces the view that CH3 radicals are the dominant growth species in microwave activated hydrocarbon/Ar/H2 gas mixtures used in the chemical vapor deposition of microcrystalline and single crystal diamond samples. [ABSTRACT FROM AUTHOR]

We recorded several rovibronic bands of C6H5O and C6D5O in their à 2B2←X 2B1 transitions in the range 1.14–1.31 μm with the cavity ringdown technique. While the electronic transition is forbidden, several vibronic bands are observed. By comparison of rovibronic contours of observed and simulated bands to determine their types of transition, and by consideration of vibrational wavenumbers of the upper state based on quantum-chemical calculations, we were able to provide vibronic assignments of observed bands and derive several experimental vibrational wavenumbers (given as ν in unit of cm-1 in this paper) for the à 2B2 state, namely, ν12=947, ν13=793, ν14=417, ν15=964, ν16=866, ν17=723, ν18=680, and ν19=499 for C6H5O, and ν12=772, ν13=626, ν14=365, ν15=812, ν17=599, ν18=532, and ν19=436 for C6D5O. Transitions involving vibrationally excited levels of ν20 were also observed; ν20 of the à state is greater by 50 cm-1 than the X state of C6H5O. A weak origin at 7681 cm-1 for the Ã←X transition of C6H5O (7661 cm-1 for C6D5O) with a c-type contour was observed. Observed isotopic ratios of vibrational wavenumbers for the à state of C6H5O to those of C6D5O are in good agreement with the predictions from quantum-chemical calculations at the B3LYP/aug-cc-pVTZ level. [ABSTRACT FROM AUTHOR]

The S1(1A′)←S0(1A′) absorption spectrum of jet-cooled 2,3-benzofluorene (Bzf) has been measured by cavity ring-down spectroscopy. The potential energy surfaces of the Sn=0,1,2 states of Bzf have been investigated with calculations based on the time-dependent density functional theory (TD-DFT). At the B3LYP/TZ level of theory, TD-DFT does not deliver a realistic difference between the excited S1 and S2 potential energy surfaces, a problem which can be avoided by introducing a reference geometry where this difference coincides with the observation. In this geometry, an expression for the Herzberg–Teller corrected intensities of the vibronic bands is proposed, allowing a straightforward assignment of the observed a′ modes below 900 cm-1, including realistic calculated intensities. For vibronic bands at higher energies, the agreement between calculated and observed modes is deteriorated by substantial Dushinsky rotations and nonparabolicities of the potential energy surface S1. [ABSTRACT FROM AUTHOR]

The nearly rotationally resolved spectrum of the à 2A′←X 2A″ 000 transition of perdeutero methyl peroxy near 1.35 μm has been studied via pulsed cavity ringdown spectroscopy. Albeit, this is a weak transition, it is possible to observe the spectrum under jet-cooled conditions (≈15 K) by combining a source of narrow-bandwidth radiation (≈250 MHz) with a supersonic slit-jet expansion incorporating an electric discharge. The near infrared radiation was obtained by using stimulated Raman scattering and a pulsed, nearly Fourier-transform-limited Ti:sapphire amplifier seeded by a scanable cw Ti:sapphire ring laser. The experimental spectrum has been fitted using a model Hamiltonian that includes the rigid body rotation of an asymmetric top and the spin-rotation interaction. An excellent quality fit was obtained resulting in the determination of 15 molecular parameters characterizing the à and X states. Other results reported for CD3O2 include an estimate of the radical concentration and the vibronic transition dipole from the observed absorption intensities. Details about the spectral linewidths are also discussed. [ABSTRACT FROM AUTHOR]

Buffer-gas pressure broadening for the ν1+ν3 band of H2O at 1.34–1.44 μm for a variety of buffer gases was investigated at room temperature using continuous-wave cavity ring-down spectroscopy. The effective interaction energy of water dimer under room temperature conditions was evaluated from the pressure broadening coefficients for rare gases using Permenter-Seaver’s relation. Monte Carlo simulations were performed using ab initio molecular orbital calculations to evaluate the interaction energies for the water dimer at 300 K. In this theoretical calculation, the orientations of the two water molecules were statistically treated. [ABSTRACT FROM AUTHOR]

• First demonstration of the detection of small amounts of methane at 8.014 µm. • Achieving the lowest detection limit of 0.063 ppb after an averaging time of 28.1 s. • Providing 1.9 times better selectivity than the frequently chosen absorption line at 7.67 µm. • Development of an OPO-DFG-based CRDS setup ensuring spectral measurements at various pressures. The paper describes the first demonstration of the detection of small amounts of methane using the 8.014 µm absorption line and cavity ring-down spectroscopy (CRDS) employing an optical parametric oscillator equipped with a differential frequency generator. The study confirmed the high stability of the system to pressure changes and the lowest detection limit of 0.063 ppb for an averaging time of 28.1 s. Experimental verification of methane spectra using a high-resolution vacuum FTIR spectrometer, tests of the developed setup presenting the influence of the wavelength resolution on the spectrum, and determining the detection limit using Alan's deviation were performed. Analysis of the achievable selectivity of methane sensors in individual water windows indicated in the range of 7.5–8.3 µm, taking into account the absorption bands of gases occurring in the standard atmosphere according to the HITRAN 2008 database was also described. Furthermore, the work presents an analysis of available solutions in the field of methane sensing, particularly on the range of longer infrared wavelengths, which showed a small number of described studies in the long wavelength infrared (LWIR) range and constituted a reference for the evaluation of the obtained result. [ABSTRACT FROM AUTHOR]

The cavity ring-down spectroscopy (CRDS) is becoming increasingly important in sensitive gas detection for atmospheric pollutant detection, greenhouse gas monitoring, human respiratory gas analysis, and measurement of specific gases in industrial processes. However, the accuracy and sensitivity of CRDS are greatly limited by noise and ring-down time extraction algorithms. To solve this problem, a CNN-assisted high-sensitivity exhaled ammonia sensor based on cavity ring-down spectroscopy was developed in this paper, which is the first time to introduce the convolutional neural network to cavity ring-down spectroscopy. A CNN filter and a neural network-based ring-down time extraction algorithm trained by two different datasets were applied to the sensor, solving the shortcomings of the traditional CRDS. Among several filters, the CNN filter achieves the best performance and the SNR is improved by 3.4 times. Compared to traditional nonlinear fitting algorithm, a sensitivity enhancement factor of 3.48 was obtained and a sub-ppb detection limit can be achieved by using Allan deviation analysis. The experimental results prove the feasibility of deep learning for improving the performance of cavity ring-down spectroscopy gas sensor. • The convolutional natural network (CNN) is firstly introduced to cavity ring-down spectroscopy. • Signal filtering and ring-down time extraction are realized simultaneously. • The exhaled ammonia sensors based on mid-infrared EC-QCL is built, and a detection limit of 0.075 ppb is obtained. [ABSTRACT FROM AUTHOR]

[Display omitted] • Q(J)-branch vibration-inversion-rotation transitions of NH 3 probed at 6.2 µm. • First experimental investigation of air-broadening for the probed transitions. • N 2 , He, Ar, and O 2 broadening coefficients measured for the probed transitions. In this experimental investigation, collision broadening effects on the Q(J)-branch vibration-inversion-rotation spectral lines of ammonia (NH 3) within the fundamental ν 4 asymmetric bending vibrational band in the 6.2 µm mid-IR region are reported. A continuous-wave external-cavity quantum cascade laser coupled with a high-sensitive cavity ring-down spectrometer was employed to selectively probe 10 transitions in high-resolution, including few inversion doublets of gaseous NH 3. Pressure-broadening coefficients, γ N H 3 - X i (X i = He, Ar, N 2, O 2, zero-air) in cm−1 atm−1, characterizing the collision interaction between NH 3 and various external perturbing gases, including helium, argon, nitrogen, oxygen, and zero-air, were determined at room temperature (296 K). Mean collision times and optical collision diameters of each collision partner were explored to gain deeper insight into the perturber-induced collision dynamics. This investigation elucidates the intricate intermolecular interactions and collision phenomena induced by various foreign perturbers with NH 3 , with potential implications for future spectroscopic and atmospheric research of this polyatomic molecule. [ABSTRACT FROM AUTHOR]

Plastic materials provide numerous benefits. However, properties such as durability and resistance to degradation that make plastic attractive for variable applications likewise foster accumulation in the environment. Fragmentation of plastics leads to the formation of potentially hazardous microplastic, of which a considerable amount derives from polystyrene. Here, we investigated the biodegradation of polystyrene by the tropical sooty mold fungus Capnodium coffeae in different experimental setups. Growth of C. coffeae was stimulated significantly when cultured in presence of plastic polymers rather than in its absence. Stable isotope tracing using 13C-enriched polystyrene particles combined with cavity ring-down spectroscopy showed that the fungus mineralized polystyrene traces. However, phospholipid fatty acid stable isotope probing indicated only marginal assimilation of polystyrene-13C by C. coffeae in liquid cultures. NMR spectroscopic analysis of residual styrene contents prior to and after incubation revealed negligible changes in concentration. Thus, this study suggests a plastiphilic life style of C. coffeae despite minor usage of plastic as a carbon source and the general capability of sooty mold fungi to stimulate polystyrene mineralization, and proposes new standards to identify and unambiguously demonstrate plastic degrading capabilities of microbes. [Display omitted] • Capnodium coffeae develops larger colonies on MP-amended semi-solid medium. • CRDS indicates slow but steady fungal 13C-PS mineralization. • PLFA stable isotope probing indicates minor PS-derived 13C-assimilation. • Generic workflow for identification of plastic biodegraders is presented. [ABSTRACT FROM AUTHOR]

• Two complementary methods applied for accurate measurements of the weak Wulf ozone bands. • New reference data for ozone cross-sections is proposed for the 9744 – 10850 cm−1 spectral range with the accuracy of 3%. • Theoretical simulation is reported using provided spin-rovibronic line lists of the singlet-triplet bands. Ozone plays a major role in atmospheric chemistry and radiative processes with an impact on climate and ecosystems being also considered as a possible biosignature species in exoplanetary observations. This makes important an extension of accurate laboratory data to various spectral ranges. The present work provides absolute absorption cross-sections of ozone accurate to about 3% in the near-IR range around 1 µm using for the first time a continuous-wave cavity-ring-down spectrometer (cw-CRDS) for recording the transitions above the first dissociation threshold of O 3. This has permitted high-sensitivity and high-resolution measurements covering the region from 9745 to 10850 cm−1 corresponding to the transitions from the electronic ground state to spin-rovibronic levels of excited triplet electronic states 3A 2 and 3B 2 that form the Wulf band system. Two complementary methods based on the stationary recording with the quasi-continuous laser tuning and on the pressure ramp measurements at carefully chosen grids of wavenumbers were implemented and provided very well consistent results within 2% on average. The experimental integrated absorption intensity in the range under the study is evaluated as 1.393×10−20 (± 2%) cm/molecule. The comparison with the available published data of continuous recordings shows that our absorption cross-sections are much more accurate, particularly in the region with complex partly resolved spin-rovibronic spectral patterns. This region corresponds to a transparency near-IR window of the water vapor and is thus well suited for atmospheric applications. The theoretical modeling of the measured spectra using eight rovibronic bands is discussed. The experimental absorption cross-sections at the dense grid of wavenumbers are provided in the electronic supplementary files, which could be used as new reference data in the 9745 to 10850 cm−1 range. [ABSTRACT FROM AUTHOR]

We have observed infrared spectra of the CF3I dimer produced in a supersonic jet by matrix-isolation Fourier transform infrared spectroscopy and infrared cavity ring-down (IR-CRD) spectroscopy. In the matrix-isolation experiments, the dimer was isolated in an Ar matrix by the pulse-deposition method. The recorded spectral range covers the symmetric (ν1) and doubly degenerate (ν4) C–F stretching regions. From the concentration dependence of the matrix-isolation spectra we have assigned one dimer band for each fundamental region. It was not easy to identify the dimer band for the ν4 band because of the multiplet feature of the monomeric ν4 band caused by the site symmetry breaking. The spectra of (CF3I)2 in the ν4 band region were thus also measured in the gas phase by IR-CRD spectroscopy, where we detected two dimer bands. Comparing the observed band positions with the results of quantum chemical calculations, we have assigned the observed dimer bands to the head-to-head isomer. The structure of (CF3I)2 and its photochemical implications are discussed, in comparison with methyl iodide dimer reported previously [Ito et al., Chem. Phys. Lett. 343, 185 (2001)]. [ABSTRACT FROM AUTHOR]

We present an extensive analysis of cavity statistics in the interior of three different proteins, in liquid n-hexane, and in water performed using molecular-dynamics simulations. The heterogeneity of packing density over atomic length scales in different parts of proteins is evident in the wide range of values observed for the average cavity size, the probability of cavity formation, and the corresponding free energy of hard-sphere insertion. More interestingly, however, the distribution of cavity sizes observed at various points in the protein interior is surprisingly homogeneous in width. That width is significantly smaller than that measured for similar distributions in liquid n-hexane or water, indicating that protein interior is much less flexible than liquid hexane. The width of the cavity size distribution correlates well with the experimental isothermal compressibility data for liquids and proteins. An analysis of cavity statistics thus provides an efficient method to quantify local properties, such as packing, stiffness, or compressibility in heterogeneous condensed media. [ABSTRACT FROM AUTHOR]

The cavity ring-down technique is used to probe the absolute optical response of the localized surface plasmon resonance (SPR) of a gold nanoparticle distribution to adsorption of trichloroethylene (TCE) and perchloroethylene (PCE) from the gas phase. Extended Mie theory for a coated sphere with a particle-size-dependent dielectric function is used to elucidate size-dispersion effects, the size-dependence of the SPR sensitivity to adsorption, and the kinetics of adsorption. An approximate Gaussian distribution of nanospheres with a mean diameter of 4.5 nm and a standard deviation of 1.1 nm, as determined by atomic force microscopy, is provided by the intrinsic granularity of an ultrathin, gold film, having a nominal thickness of ≈0.18 nm. The cavity ring-down measurements employ a linear resonator with an intracavity flow cell, which is formed by a pair of ultrasmooth, fused-silica optical flats at Brewster’s angle, where the Au film is present on a single flat. The total system intrinsic loss is dominated by the film extinction, while the angled flats alone contribute only ≈5×10[sup -5]/flat to the total loss. Based on a relative ring-down time precision of 0.1% for ensembles averages of 25 laser shots from a pulsed optical parametric oscillator, the minimum detectable concentrations of PCE and TCE obtained by probing the SPR response are found to be 2 and 7×10[sup -8] mol/L, respectively, based on a 30 s integration time. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Infrared cavity ringdown laser absorption spectroscopy was used to characterize the gas-phase HCl and DCl stretch modes of three small acid-water clusters at 0.04 cm[sup -1] resolution. The H[sup 35]Cl stretch of HClH[sub 2]O at 2723.1 cm[sup -1] and the D[sup 35]Cl stretch for DClD[sub 2]O and DCl(D[sub 2]O)[sub 2] were found to be at 1976.0 and 1796.7 cm[sup -1], respectively. The spectral shifts with respect to the HCl and DCl monomers are consistent with theoretical predictions and matrix isolation work. Rotational structure was resolved for DClD[sub 2]O and spectroscopic constants for both chlorine isotopomers were determined. The spectral shifts and band shapes were similar to those observed for the bonded OH stretch of pure water clusters. Cluster number densities (∼1 × 10[sup 12] cm[sup -3]) were slightly lower than found for the pure water clusters under similar conditions. Predissociation and IVR broadening in the acid-water clusters were determined to be qualitatively similar to the case of pure water and DF clusters. [ABSTRACT FROM AUTHOR]

Cavity ring down spectroscopy (CRDS) was used for measuring absolute concentration profiles of the CN (cyano) radical during oxyacetylene flame deposition of diamond. Profiles were measured for three different nitrogen additions to the flame. Novel ways for the determination of the lateral position of the laser beam and its height above the deposition substrate are presented. Measured column density profiles show that the influence of added nitrogen is limited to a central area within a radius of 2.7 mm. Outside this area the profiles are hardly influenced by the added nitrogen flow. Comparison with work of S. J. Firchow and K. L. Menningen [J. Phys. D: Appl. Phys. 32, 937 (1999)] shows a good correspondence. Absolute concentration profiles were obtained by applying Abel inversion processing and using a temperature distribution resulting from numerical simulations. The resulting profiles show an off-axis maximum for all three nitrogen additions. With an increasing nitrogen addition the maximum and central concentrations also increased. Upon inspection of the profiles it follows that the gas phase above the deposition area can be divided into three sections: a central one in which the added nitrogen is the dominant nitrogen source, an outer one where the nitrogen from the ambient plays a dominant role, and an intermediate zone where both nitrogen sources have a significant influence. The latter is the area in which the maxinmm of the CN concentration is situated. Previous laser-induced fluorescence (LIF) profiles of CN, measured under very similar experimental conditions, show similar distributions. Differences between the CRDS and LIF results are discussed. [ABSTRACT FROM AUTHOR]

Cavity ring-down spectroscopy has been used to measure the absorbances, concentrations and temperatures of C[SUB2](a[SUP3]Π[SUBu] υ = 0) and CH(X[SUP2]Π υ = 0) radicals in a &les;10 kW dc arc jet used for chemical vapor deposition (CVD) of polycrystalline diamond films and operated with CH[SUB4]/H[SUB2]/Ar gas mixtures. Gas temperatures derived from the intensities and widths of rotationally resolved C[SUB2] d[SUP3]Π[SUBg]-a[SUP3]Π[SUBu] spectral lines are 3300±200 K in the free plume, rising to ~4800 K close to the substrate on which the diamond film is grown. For an input power of ~6 kW, a 3.3% CH[SUB4]/H[SUB2] ratio with excess Ar and a pressure of 50 Torr, the conditions typically employed for diamond film CVD, concentrations of C[SUB2](a) are between 6.0±0.2×10[SUP12] and 1.5±0.2×10[SUP13] cm[SUP-3] in the fr'ee plume at distances >5 mm from the substrate. These values are derived assuming a 1 cm column length as implied by spatially resolved studies of C[SUB2](d-a) optical emission; the spread reflects the decline in performance of the arc jet torch heads over time. The concentration of CH(X) in the free plume is 7.0±1.3×10[SUP12] cm[SUP-3] under similar operating conditions. Within 5 mm of the substrate, the measured absorption by both radicals rises steeply. The concentrations of C[SUB2](a) and CH(X) increase with added CH[SUB4] at fixed powers of 5.5 and 5.8 kW, but for mixing ratios in excess of 5% CH[SUB4]/H[SUB2], the concentrations of both radicals become invariant. Measured C[SUB2](a) absorbance also increases with power input to the arc jet, but the CH absorbance is independent of this operating parameter. [ABSTRACT FROM AUTHOR]

The ν[sub 2] + 2ν[sub 3] combination band of [sup 12]CH[sub 4] near 7510 cm[sup -1] was studied with the recently introduced technique of cavity ring-down spectroscopy employing a cw-diode laser in a pulsed supersonic slit jet expansion and with Doppler-limited Fourier-transform infrared spectroscopy at room temperature. ν[sub 2] + 2ν[sub 3] is the strongest absorption band in the high-wave-number region of the N = 2.5 icosad of methane. First assignments of the combination band are provided. The vibrational origin of ν[sub 2] + 2ν[sub 3] at 7510.3378±0.0010 cm[sup -1], the integrated band strength G = (1.3±0.2) x10[sup -4] pm² and the vibrational transition moment μ[sub ν] = (1.0±0.1)x10[sup -3] D have been determined. The values represent benchmarks to test effective vibrational Hamiltonians and ab initio calculations for methane. Although an isolated band analysis was possible at low J-values, the influence of strong perturbations becomes evident at higher rotational excitation. The F[sub 1]-component of ν[sub 2] + 2ν[sub 3] interacting by a strong Coriolis resonance with the IR-active F[sub 2]-component appears to be a dominant perturber. [ABSTRACT FROM AUTHOR]

We investigate the optical transmission of a tilted plane Fabry-Perot cavity leading to spatial cavity ringdown, the exponentially decaying intensity output present along the transverse spatial coordinate. Primary features of the spatial cavity ringdown are theoretically predicted from the spectral and spatial cavity transfer function which is derived analytically on the combined basis of ray optics and diffraction theory applied to an ideal diffraction lossless cavity of one transverse dimension. Spatial frequency filtration by a narrow Lorentzian-shaped cavity resonance is shown to play key roles on the spatial aspects of transmitted beam profiles. Our theoretical formulation is further extended to the case of wedged plane Fabry-Perot cavities. The experimental observation of spatial cavity ringdown signals exhibits an excellent agreement with the theoretical prediction. [ABSTRACT FROM AUTHOR]

We report measurements of the water vapor continuum using infrared cavity ringdown spectroscopy at frequencies of 931.002, 944.195, and 969.104 cm[sup -1]. Our values of the water vapor continuum coefficients for self-broadening at T=296K are C[sup 0, sub s] (931cm[sup -1])=2.23±0.17, C[sup 0, sub s](944cm[sup -1]) = 2.02±0.13, and C[sup 0, sub s](969 cm[sup -1]) = 1.79±0.21 x 10[sup -22] molecules[sup -1] cm² atm[sup -1]. Our measurements are found to be in good agreement with the far wing line shape theory of Ma and Tipping, but we find that empirical models of the water vapor continuum, widely used in radiative transfer calculations, significantly overestimate the observed self-broadened continuum. [ABSTRACT FROM AUTHOR]

Cavity ring down absorption spectroscopy is applied for the detection of Si and SiH radicals in a remote Ar-H[sub 2]-SiH[sub 4] plasma used for high rate deposition of device quality hydrogenated amorphous silicon (a-Si:H). The formation and loss mechanisms of SiH in the plasma are investigated and the relevant plasma chemistry is discussed using a simple one-dimensional model. From the rotational temperature of SiH typical gas temperatures of ∼1500 K are deduced for the plasma, whereas total ground state densities in the range of 10[sup 15]-10[sup 16] m[sup -3] for Si and 10[sup 16]-10[sup 17] m[sup -3] for SiH are observed. It is demonstrated that both Si and SiH have only a minor contribution to a-Si:H film growth of ∼0.2% and ∼2%, respectively. From the reaction mechanisms in combination with optical emission spectroscopy data, it is concluded that Si and SiH radicals initiate the formation of hydrogen deficient polysilane radicals. In this respect, Si and SiH can still have an important effect on the a-Si:H film quality under certain circumstances. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Reports on the recording of the cavity ringdown (CRD) spectrum of the thiophosgene absorption system under supersonic jet conditions to obtain insights into the photophysical properties of collision-free thiophosgene. Decay of thiophosgene by the nonradiative intersystem crossing; Estimated nonradiative life.

Measures the quantitative absorption spectra and determines the integrated absorption intensity band by the use of cavity ringdown spectroscopy and high-resolution, long-path Fourier transform (FT) spectroscopy. Conversion of the raw data from the FT spectrometer to transmittance spectra; Ringdown rate coefficient.

Negative ion source is a core part of the neutral beam injection system for magnetic confinement fusion devices. The density of produced hydrogen negative ions is a critical parameter of the negative ion source. Cavity ring-down spectroscopy (CRDS) is an ultrasensitive absorption diagnostic technique for density measurement. Based on the photodetachment process, CRDS can measure the integrated line-of-sight hydrogen negative ion density in a high power ion source. The CRDS diagnostic system has been applied to Hefei utility negative ion test equipment with the radio frequency (RF) source, which is now one of the references for the China Fusion Engineering Test Reactor neutral beam injection system. Typical ring-down signals are obtained to calculate the density of hydrogen negative ions. The time evolution of hydrogen negative ion density is successfully measured. Preliminary experiments show the accurate relationship between RF power and measured hydrogen negative ion density. [ABSTRACT FROM AUTHOR]

According to the latest physics design of the China Fusion Engineering Test Reactor (CFETR), two neutral beam injectors (NBIs), which deliver a total of 40 MW in not less than 3600 s with 1 MeV D0, are demanded to support current drive and plasma rotation. To minimize the risks and time to provide the CFETR with reliable NBIs, a negative NBI test facility will be developed at the Institute of Plasma Physics, Chinese Academy of Science. Its mission is to understand the characteristics of the RF driven ion source and negative ion generation and extraction and to improve RF efficiency and beam quality. In order to achieve this goal, a set of diagnostic tools will be used in this test facility. For source diagnostics, optical emission spectroscopy, cavity ring-down spectroscopy, laser absorption spectroscopy, and electrostatic probes are planned to be used. Beam emission spectroscopy, W-wire calorimeters, 1D carbon fiber composite diagnostic calorimeters, beam dump with thermocouples, and water-flow calorimetry are used to assess the beam properties. The design of the diagnostic system is presented. [ABSTRACT FROM AUTHOR]

For the past two decades, the measurement of N2O isotopocules - isotopically substituted molecules14N15N16O,15N14N16O and14N14N18O of the main isotopic species14N14N16O - has been a promising technique for understanding N2O production and consumption pathways. The coupling of non-cryogenic and tuneable light sources with different detection schemes, such as direct absorption quantum cascade laser absorption spectroscopy (QCLAS), cavity ring-down spectroscopy (CRDS) and off-axis integrated cavity output spectroscopy (OA-ICOS), has enabled the production of commercially-available and field-deployable N2O isotopic analyzers. In contrast to traditional isotope-ratio mass-spectrometry (IRMS), these instruments are inherently selective for position-specific15N substitution and provide real-time data, with minimal or no sample pretreatment, which is highly attractive for process studies. Here, we compared the performance of N2O isotope laser spectrometers with the three most common detection schemes: OA-ICOS (N2OIA-30e-EP, ABB-Los Gatos Research Inc.), CRDS (G5131-i, Picarro Inc.) and QCLAS (dual QCLAS and preconcentration (TREX)-mini QCLAS, Aerodyne Research Inc.). For each instrument, the precision, drift and repeatability of N2O mole fraction [N2O] and isotope data were tested. The analyzers were then characterized for their dependence on [N2O], gas matrix composition (O2, Ar) and spectral interferences caused by H2O, CO2, CH4 and CO to develop analyzer-specific correction functions. Subsequently, a simulated two end-member mixing experiment was used to compare the accuracy and repeatability of corrected and calibrated isotope measurements that could be acquired using the different laser spectrometers. Our results show that N2O isotope laser spectrometer performance is governed by an interplay between instrumental precision, drift, matrix effects and spectral interferences. To retrieve compatible and accurate results, it is necessary to include appropriate reference materials following the identical treatment (IT) principle during every measurement. Remaining differences between sample and reference gas compositions have to be corrected by applying analyzer-specific correction algorithms. These matrix and trace gas correction equations vary considerably according to N2O mole fraction, complicating the procedure further. Thus, researchers should strive to minimize differences in composition between sample and reference gases. In closing, we provide a calibration workflow to guide researchers in the operation of N2O isotope laser spectrometers in order to acquire accurate N2O isotope analyses. We anticipate that this workflow will assist in applications where matrix and trace gas compositions vary considerably (e.g. laboratory incubations, N2O liberated from wastewater or groundwater), as well as extending to future analyzer models and instruments focusing on isotopic species of other molecules. [ABSTRACT FROM AUTHOR]

Carbon dioxide and oxygen are tightly coupled in land biosphere CO2 – O2 exchange processes, whereas they are not coupled in oceanic exchange. For this reason, atmospheric oxygen measurements can be used to constrain the global carbon cycle, especially oceanic uptake. However, accurately quantifying small (∼1 –100 ppm) variations in O2 is analytically challenging due to the very large atmospheric background which constitutes about 20.9 % (∼209500 ppm) of atmospheric air. Here we present a detailed description of a newly developed high-precision oxygen mixing ratio and isotopic composition analyzer (Picarro G2207) that is based on cavity ring-down spectroscopy (CRDS) as well as to its operating principles; we also demonstrate comprehensive laboratory and field studies using the abovementioned instrument. From the laboratory tests, we calculated a short-term precision (standard error of 1 min O2 mixing ratio measurements) of < 1 ppm for this analyzer based on measurements of eight standard gases analyzed for 2 h, respectively. In contrast to the currently existing techniques, the instrument has an excellent long-term stability; therefore, calibration every 12 h is sufficient to get an overall uncertainty of < 5 ppm. Measurements of ambient air were also conducted at the Jungfraujoch high-altitude research station and the Beromünster tall tower in Switzerland. At both sites, we observed opposing and diurnally varying CO2 and O2 profiles due to different processes such as combustion, photosynthesis, and respiration. Based on the combined measurements at Beromünster tower, we determined height-dependent O2:CO2 oxidation ratios varying between -0.98 and -1.60 ; these ratios increased with the height of the tower inlet, possibly due to different source contributions such as natural gas combustion, which has a high oxidation ratio, and biological processes, which have oxidation ratios that are relatively lower. [ABSTRACT FROM AUTHOR]