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We present the theory and experimental details for chiral-cavity-ring-down polarimetry and magnetometry, based on ring cavities supporting counterpropagating laser beams. The optical-rotation symmetry is broken by the presence of both chiral and Faraday birefringence, giving rise to signal reversals which allow rapid background subtractions. We present the measurement of the specific rotation at 800 nm of vapors of a-pinene, 2-butanol, and a-phellandrene, the measurement of optical rotation of sucrose solutions in a flow cell, the measurement of the Verdet constant of fused silica, and measurements and theoretical treatment of evanescent-wave optical rotation at a prism surface. Therefore, these signal-enhancing and signal-reversing methods open the way for ultrasensitive polarimetry measurements in gases, liquids and solids, and at surfaces. [ABSTRACT FROM AUTHOR]

We integrated a rigid optical trap into a tunable pulsed cavity ringdown spectroscopy (OT-CRDS) system to characterize the extinction of single airborne particles in the UV spectral region (306-315 nm). Single solid particles from a multi-walled carbon nanotube (MWCNT), Bermuda grass smut spore, carbon microsphere, and blackened polyethylene microsphere were trapped in air based on the photophoretic force. The improved OT-CRDS system was highly sensitive and able to resolve extinctions of single particles from different materials and sizes at a given wavelength. Further, we successfully manipulated the number of particles, e.g., 1, 2 or more particles, in the trap and measured their distinguishable extinctions using the OT-CRDS. We also show that the particle size and extinction have a good linear correlation from the measurements of 24 single MWCNT particles. Material- and wavelength-dependent extinctions of the four types of airborne particles were also characterized. Results reveal that single airborne particles regardless of their differences in material and size, due to their heterogeneous morphology, have individual-particle dependent extinctions and that dependence can be resolved and characterized using the OT-CRDS technique.

The reference method to quantify mixing ratios of the criteria air pollutant nitrogen dioxide (NO 2) is NO-O 3 chemiluminescence (CL), in which mixing ratios of nitric oxide (NO) are measured by sampling ambient air directly, and mixing ratios of NO x (= sum of NO and NO 2) are measured by converting NO 2 to NO using, for example, heated molybdenum catalyst or, more selectively, photolytic conversion (P-CL). In this work, the nitrous acid (HONO) interference in the measurement of NO 2 by P-CL was investigated. Results with two photolytic NO 2 converters are presented. The first used radiation centered at 395 nm, a wavelength region commonly utilized in P-CL. The second used light at 415 nm, where the overlap with the HONO absorption spectrum and hence its photolysis rate are less. Mixing ratios of NO 2 , NO x and HONO entering and exiting the converters were quantified by Thermal Dissociation Cavity Ring-down Spectroscopy (TD-CRDS). Both converters exhibited high NO 2 conversion efficiency (CF NO2 ; > 90%) and partial conversion of HONO. Plots of CF against flow rate were consistent with photolysis frequencies of 4.2 s-1 and 2.9 s-1 for NO 2 and 0.25 s-1 and 0.10 s−1 for HONO at 395 nm and 415 nm, respectively. CF HONO was larger than predicted from the overlap of the emission and HONO absorption spectra. The results imply that measurements of NO 2 by P-CL marginally but systematically overestimate true NO 2 concentrations, and that this interference should be considered in environments with high HONO:NO 2 ratios such as the marine boundary layer or in biomass burning plumes. [Display omitted] [ABSTRACT FROM AUTHOR]

Photoacoustic spectroscopy technology is an important method to detect the concentration of trace gases, so it is of great significance to improve the detection accuracy of the photoacoustic spectroscopy system (PAS). In this paper, a multiple linear regression algorithm was proposed to correct the accuracy of the PAS based on the high-precision cavity ring-down spectroscopy measurement system. The results showed that the correlation coefficient R2 between the corrected values of the multiple linear regression model and the reference true values was 0.903. It can be seen that the algorithm can effectively improve the detection accuracy of the PAS. A comparative experiment was carried out with the long optical path differential absorption spectroscopy system (LP-DOAS) for measuring the NO2 concentration in an ambient atmosphere. The experimental results showed that the corrected PAS and the LP-DOAS had a good correlation in measuring the NO2 concentration, the slope of linear fitting was 1.012 ± 0.040, and the correlation coefficient was 0.948. [ABSTRACT FROM AUTHOR]

We present measurements of isoprene-derived organic nitrates (ISOP-NITs) generated in the reaction of isoprene with the nitrate radical (NO 3) in a 1 m 3 Teflon reaction chamber. Detection of ISOP-NITs is achieved via their thermal dissociation to nitrogen dioxide (NO 2), which is monitored by cavity ring-down spectroscopy (TD-CRDS). Using thermal dissociation inlets (TDIs) made of quartz, the temperature-dependent dissociation profiles (thermograms) of ISOP-NITs measured in the presence of ozone (O 3) are broad (350 to 700 K), which contrasts the narrower profiles previously observed for, for example, isopropyl nitrate (iPN) or peroxy acetyl nitrate (PAN) under the same conditions. The shape of the thermograms varied with the TDI's surface-to-volume ratio and with material of the inlet walls, providing clear evidence that ozone and quartz surfaces catalyse the dissociation of unsaturated organic nitrates leading to formation of NO 2 at temperatures well below 475 K, impeding the separate detection of alkyl nitrates (ANs) and peroxy nitrates (PNs). The use of a TDI consisting of a non-reactive material suppresses the conversion of isoprene-derived ANs at 473 K, thus allowing selective detection of PNs. The potential for interference by the thermolysis of nitric acid (HNO 3), nitrous acid (HONO) and O 3 is assessed. [ABSTRACT FROM AUTHOR]

Nitrogen dioxide (14NO 2) exhibits a unique doublet structure due to the presence of its unpaired electron, which results in a nonzero electronic angular momentum in the ground electronic state of the molecule. In this study, an investigation into high-resolution rovibrational spectral features associated with the spin-rotation doublets of 14NO 2 was conducted using an external-cavity quantum cascade laser (EC-QCL)-coupled cavity ring-down spectrometer operating at 6.2 μm. Four spin-split doublets belonging to the RR branch of the (0 0 1)-(0 0 0) fundamental band were probed in the mid-IR spectral region. The air broadening and self-broadening coefficients were reported explicitly for each doublet component for the first time, to the best of our knowledge. The line-intensities were also quantified, and they were compared to the HITRAN database, revealing good agreement (<4% discrepancy). [ABSTRACT FROM AUTHOR]

We present the results of the spectral line-shape study of the first measurement of the extremely weak (7–0) band of the 12C16O molecule. Measurements were done with a highly sensitive cavity ring-down spectrometer. Collisional narrowing, analyzed in terms of speed-dependent effects, was observed for the first time for transitions with line intensities below 2 ⋅ 1 0 − 29 cm/molecule at 296 K. We provide a full set of line-shape parameters of the speed-dependent and regular Voigt profile analysis for 14 transitions from P and R branches. Experimental verification of a strong vibrational dependence of the pressure shifting described by the Hartmann model (Hartmann, 2009) is extended up to the sixth overtone highly sensitive to the model parameter. [Display omitted] • The first line-shape study of the extremely weak (7–0) band of the 12C16O molecule. • Speed-dependent effects observed for transitions with intensities below 2 ⋅ 1 0 − 29 cm/molecule. • Full set of line-shape parameters of the speed-dependent and regular Voigt profile analysis. • Experimental verification of a strong vibrational dependence of the pressure shifting described by the Hartmann model. [ABSTRACT FROM AUTHOR]

The first characterization of the monomer bending vibrations in gaseous water clusters was conducted by using infrared cavity ringdown spectroscopy. Discrete and sequentially blue-shifted bands near 6 microns for n = 2-4 and unresolved broad features for n > 4, supporting both theoretical computations and solid-state spectroscopy results were obtained. These measurements offer a measure of the monomer distortion that accompanies sequential hydrogen bond formation.

The isotopic composition of precipitation (δ18O, δ2H, and δ17O) is affected by evaporation and exchange as hydrometeors descend. These processes can significantly alter the isotopic ratio of precipitation relative to its initial condensation state in the cloud yet are exceedingly difficult to study in situ. The most widely utilized model for droplet‐atmosphere exchange was derived from controlled experiments where droplets were suspended by forced air in a narrow glass tube‐ a design that manipulated the structure of the boundary layer around the droplet. Here, we provide a novel experimental test of atmosphere‐hydrometeor isotopic exchange using the mechanism of acoustic levitation, where sound waves are projected vertically to levitate droplets in free‐flowing ambient air. We present results from a series of droplet levitation experiments where the droplets' surface temperatures were measured by a thermal camera and the background atmospheric isotope concentration was measured via cavity‐ringdown spectroscopy, providing a high degree of constraint on the fractionation conditions. We show that isotope enrichment of the suspended droplets met first order expectations based on existing models. However, to account for the slope of δ18O versus δ2H (i.e., the meteoric water line) and deuterium excess of the droplets as they evolved, we had to modify the existing model for droplet‐atmosphere exchange to account for the fact that some portion of the evaporative flux from the droplet remained present in the boundary layer around the droplet leading to an evolving feedback between droplet and the atmosphere‐that is, a quasi closed‐system effect. The isotopic enrichment of the boundary layer surrounding the droplet as a consequence of the closed‐system dynamics, drives more rapid δ18O isotope enrichment relative to δ2H of the droplet compared to what is predicted using an open system model. Although these were controlled experiments, they illustrate important dynamics regarding the isotopic signature of feedbacks between droplet evaporation and atmospheric humidity. [ABSTRACT FROM AUTHOR]

Skin cells emit volatile organic compounds (VOCs), and some of them can be used as biomarkers for screening specific diseases. Dimethyl disulfide (DMDS) has been recently reported as a biomarker of melanoma skin cancer (Kwak et al. "Volatile Biomarkers from Human Melanoma Cells". J. Chromatogr. B. 2013. 931: 90-96.). With the motivation of diagnosing melanoma using DMDS as its biomarker, we explore the potential of measuring DMDS using an advanced laser spectroscopic technique as an alternative method. We report on the first DMDS measurements using an experimental system based on cavity ringdown spectroscopy (CRDS). The test samples were mixtures of DMDS vapor and nitrogen in different concentrations. Two sampling methods were investigated to dilute the DMDS sample to low concentrations for ringdown measurements. The results showed that the ringdown system responded to various DMDS concentrations linearly and a theoretical detection limit of sub-ppb (parts per billion) could be achieved at the absorption wavelength of 266 nm. This ringdown system exhibited a high dynamic range for DMDS measurements, from ppm (parts per million) to ppt (parts per trillion) levels, given different laser wavelengths used. The feasibility of developing a portable melanoma screening sensor using the CRDS technique was also demonstrated in this study., (© The Author(s) 2016.)

Abstract: The absorption spectra of jet-cooled AsH2 radicals were recorded in the wavelength range of 435–510nm by cavity ringdown spectroscopy. The AsH2 radicals were produced by pulsed DC discharge in a molecular beam of a mixture of AsH3, SF6, and argon. Seven vibronic bands with fine rotational structures have been identified and assigned as the , , and (n =1–3) bands of the electronic transition. Based on the previous studies of AsH2 radical, rotational assignments and rotational term values for each band were obtained, and the molecular parameters including vibrational constants, rotational constants, centrifugal distortion constants, and spin–rotation interaction constants were also determined. [Copyright &y& Elsevier]

Abstract: The plasma plume induced by dual-pulse laser ablation of a titanium target in vacuum was analyzed by the technique of cavity ringdown spectroscopy (CRDS). Large Doppler-splitting of the absorption spectral lines was observed which is due to increase of the velocity components parallel to the optical axis and specific features of the CRDS measurements. Vertical velocity component, the particle number density and plasma volume also show increase compared to the single-pulse laser ablation. The forward convolution best fit of absorption lineshapes was used to extract parameters describing dual-pulse laser ablation plasma plume. [Copyright &y& Elsevier]

Rationale: The accuracy determined in the routine analysis of water isotopes (δ17O, δ18O, δ2H) using cavity ring‐down spectroscopy is greatly affected by the memory effect (ME), a sample‐to‐sample carryover that biases measurements. This study aims to develop a simple method that rapidly removes the ME. Methods: We developed a method, designed for the Picarro L2140‐i, that removes the ME by injecting small amounts of water with an extreme isotopic value ("kick") in the opposite direction of the ME. We conducted 11 experiments to identify the optimal kick for pairs of isotopically enriched and depleted samples. Once quantified, the optimal kick was used to create an ME‐free, unbiased calibration curve, which was verified using international and internal lab standards. Results: Our kick method removes the ME very efficiently in half the time it takes for experiments without a kick. The optimal number of kick injections required to minimize stabilization time between standards of different compositions is three injections of δ2H ≈ −1000‰ water per a 100‰ difference between standards. Three runs of routine measurements using the kick method resulted in uncertainties of 0.03‰, 0.2‰, and 5 permeg for δ18O, δ2H, and 17O‐excess, respectively. Conclusions: This study demonstrates a new method for rapidly removing the ME. Our kick protocol is a readily available, cheap, and efficient approach to reduce instrumental bias and improve measurement accuracy. [ABSTRACT FROM AUTHOR]

The carbon isotope composition of respired CO2 (δ13CR) and bulk organic matter (δ13CB) of various plant compartments informs about the isotopic fractionation and substrate of respiratory processes, which are crucial to advance the understanding of carbon allocation in plants. Nevertheless, the variation across organs, species and seasons remains poorly understood. Cavity Ring-Down Laser Spectroscopy was applied to measure δ13CR in leafy shoots and woody stems of maple (Acer platanoides L.), oak (Quercus robur L.) and cedar (Thuja occidentalis L.) trees during spring and late summer. Photosynthesis, respiration, growth and non-structural carbohydrates were measured in parallel to evaluate potential drivers for respiratory fractionation. The CO2 respired by maple and oak shoots was 13C-enriched relative to δ13CB during spring, but not late summer or in the stem. In cedar, δ13CR did not vary significantly throughout organs and seasons, with respired CO2 being 13C-depleted relative to δ13CB. Shoot δ13CR was positively related to leaf starch concentration in maple, while stem δ13CR was inversely related to stem growth. These relations were not significant for oak or cedar. The variability in δ13CR suggests (i) different contributions of respiratory pathways between organs and (ii) seasonality in the respiratory substrate and constitutive compounds for wood formation in deciduous species, less apparent in evergreen cedar, whose respiratory metabolism might be less variable. [ABSTRACT FROM AUTHOR]

With an atmospheric concentration of approximately 2000 parts per billion (ppbV, 10 -9), methane (CH 4) is the second most abundant greenhouse gas (GHG) in the atmosphere after carbon dioxide (CO 2). The task of long-term and spatially resolved GHG monitoring to verify whether climate policy actions are effective is becoming more crucial as climate change progresses. In this paper we report the CH 4 concentration readings of our photoacoustic (PA) sensor over a 5 d period at Hohenpeißenberg, Germany. As a reference device, a calibrated cavity ring-down spectrometer, Picarro G2301, from the meteorological observatory of the German Weather Service (DWD) was employed. Trace gas measurements with photoacoustic instruments promise to provide low detection limits at comparably low costs. However, PA devices are often susceptible to cross-sensitivities related to fluctuating environmental conditions, e.g. ambient humidity. The obtained results show that for PA sensor systems non-radiative relaxation effects induced by varying humidity are a non-negligible factor. Applying algorithm compensation techniques, which are capable of calculating the influence of non-radiative relaxation effects on the photoacoustic signal, increase the accuracy of the photoacoustic sensor significantly. With an average relative deviation of 1.11 % from the G2301, the photoacoustic sensor shows good agreement with the reference instrument. [ABSTRACT FROM AUTHOR]

Dark CO 2 fixation by bacteria is believed to be particularly important in oligotrophic ecosystems. However, only a few studies have characterized the role of bacterial dissolved inorganic carbon (DIC) fixation in global carbon dynamics. Therefore, this study quantified the primary production (PP), total bacteria dark CO 2 fixation (TB DIC fixation), and heterotrophic bacterial production (HBP) in the warm and oligotrophic Red Sea using stable-isotope labeling and cavity ring-down spectroscopy (13 C–CRDS). Additionally, we assessed the contribution of bacterial DIC fixation (TB DIC %) relative to the total DIC fixation (total DIC fixation). Our study demonstrated that TB DIC fixation increased the total DIC fixation from 2.03 to 60.45 µ g C L -1 d -1 within the photic zone, contributing 13.18 % to 71.68 % with an average value of 33.95 ± 0.02 % of the photic layer total DIC fixation. The highest TB DIC fixation values were measured at the surface and deep (400 m) water with an average value of 5.23 ± 0.45 and 4.95 ± 1.33 µ g C L -1 d -1 , respectively. These findings suggest that the non-photosynthetic processes such as anaplerotic DIC reactions and chemoautotrophic CO 2 fixation extended to the entire oxygenated water column. On the other hand, the percent of TB DIC contribution to total DIC fixation increased as primary production decreased (R2=0.45 , p<0.0001), suggesting the relevance of increased dark DIC fixation when photosynthetic production was low or absent, as observed in other systems. Therefore, when estimating the total carbon dioxide production in the ocean, dark DIC fixation must also be accounted for as a crucial component of the carbon dioxide flux in addition to photosynthesis. [ABSTRACT FROM AUTHOR]

The electronic transition spectra of the indene molecular cation (In + , C 9 H 8 + ) in the 550–580 nm region has been measured in the gas phase in direct absorption. The spectra were experimentally recorded using sensitive cavity ring-down spectroscopy in a supersonically expanding planar plasma. Two lifetime-broadened vibronic bands are assigned to the 2 A ′ ′ - X 2 A ′ ′ electronic transition system of In + . A set of indicative spectroscopic parameters have been obtained from a band contour analysis of the 0 0 0 band in combination with supporting ab-initio calculations. The inferred Lorentz line width of 4.0 ± 0.5 cm − 1 indicates an upper state lifetime of 1.2 ± 0.1 ps . The laboratory data are compared to the diffuse interstellar bands (DIBs), and no matches can be found. Upper limits for In + column densities in the diffuse interstellar medium have also been estimated from six sightline spectra. [ABSTRACT FROM AUTHOR]

We monitored stable water isotopes in liquid precipitation and atmospheric water vapour (δv) using in situ cavity ring‐down spectroscopy (CRDS) over a 2 month period in an urban green space area in Berlin, Germany. Our aim was to better understand the origins of atmospheric moisture and its link to water partitioning under contrasting urban vegetation. δv was monitored at multiple heights (0.15, 2 and 10 m) in grassland and forest plots. The isotopic composition of δv above both land uses was highly dynamic and positively correlated with that of rainfall indicating the changing sources of atmospheric moisture. Further, the isotopic composition of δv was similar across most heights of the 10 m profiles and between the two plots indicating high aerodynamic mixing. Only at the surface at ~0.15 m height above the grassland δv showed significant differences, with more enrichment in heavy isotopes indicative of evaporative fractionation especially after rainfall events. Further, disequilibrium between δv and precipitation composition was evident during and right after rainfall events with more positive values (i.e., values of vapour higher than precipitation) in summer and negative values in winter, which probably results from higher evapotranspiration and more convective precipitation events in summer. Our work showed that it is technically feasible to produce continuous, longer‐term data on δv isotope composition in urban areas from in situ monitoring using CRDS, providing new insights into water cycling and partitioning across the critical zone of an urban green space in Central Europe. Such data have the potential to better constrain the isotopic interface between the atmosphere and the land surface and to thus, improve ecohydrological models that can resolve evapotranspiration fluxes. [ABSTRACT FROM AUTHOR]

Rovibrationally resolved spectra of the Nj=22, Ka=0←1 transition and of the Nj=23, Ka=0←0 and Ka=1←0 transitions of the hydrogen‐bonded (HF)2 have been measured in the near infrared range near 1.3 μm by cw‐diode laser cavity ring‐down spectroscopy in a pulsed supersonic slit jet expansion. The spectroscopic assignment and analysis provided an insight into the dynamics of these highly‐excited vibrational states, in particular concerning the predissociation of the hydrogen bond and the tunneling process of the hydrogen bond switching. Together with our previously analyzed spectra of the Nj=21 and Nj=22 components, the mode‐specific dynamics in all three components of this triad can now be compared. In the N=2 triad, the HF‐stretching vibration is excited by two quanta with similar excitation energy, but the quanta are distributed in three different ways, which has a distinct influence on the dynamics. The observed band centers and tunneling splittings are in agreement with our recent calculations on the (HF)2 potential energy hypersurface SO‐3, resolving the long‐standing discussion about the symmetry ordering of polyad levels in this overtone region. The results are also discussed in relation to the general questions of non‐statistical reaction dynamics of polyatomic molecules and clusters and in relation to quasi‐adiabatic channel above barrier tunneling. [ABSTRACT FROM AUTHOR]

Nitrogen (N) is a key nutrient required by all living organisms for growth and development, but is a limiting resource for many organisms. Organisms that feed on material with low N content, such as wood, might be particularly prone to N limitation. In this study, we investigated the degree to which the xylophagous larvae of the stag beetle Ceruchus piceus (Weber) use associations with N-fixing bacteria to acquire N. We paired acetylene reduction assays by cavity ring-down absorption spectroscopy (ARACAS) with 15N2 incubations to characterize rates of N fixation within C. piceus. Not only did we detect significant N fixation activity within C. piceus larvae, but we calculated a rate that was substantially higher than most previous reports for N fixation in insects. While taking these measurements, we discovered that N fixation within C. piceus can decline rapidly in a lab setting. Consequently, our results demonstrate that previous studies, which commonly keep insects in the lab for long periods of time prior to and during measurement, may have systematically under-reported rates of N fixation in insects. This suggests that within-insect N fixation may contribute more to insect nutrition and ecosystem-scale N budgets than previously thought. [ABSTRACT FROM AUTHOR]

Rationale: The precision obtained in routine isotope analysis of water (δ17O, δ18O, δ2H, 17O‐excess and d‐excess values) using cavity ring‐down spectroscopy is usually below the instrument specifications provided by the manufacturer. This study aimed at reducing this discrepancy, with particular attention paid to mitigating the memory effect (ME). Methods: We used a Picarro L2140i analyzer coupled with a high‐precision A0211 vaporizer and an A0325 autosampler. The magnitude and duration of the ME were estimated using 24 series of 50 successive injections of samples with contrasting compositions. Four memory correction methods were compared, and the instrument performance was evaluated over a 17‐month period of routine analysis, using two different run architectures. Results: The ME remains detectable after the 30th injection, implying that common correction procedures only based on the last preceding sample need to be revised. We developed a new ME correction based on the composition of several successive samples, and designed a run architecture to minimize the magnitude of the ME. The standard deviation obtained from routine measurement of a quality assurance water sample over a seven‐month period was 0.015‰ for δ17O, 0.023‰ for δ18O, 0.078‰ for δ2H, 0.006‰ for 17O‐excess and 0.173‰ for d‐excess. In addition, we provided the first δ17O and 17O‐excess values for the GRESP certified reference material. Conclusions: This study demonstrates the long‐term persistence of the ME, which is often overlooked in routine analysis of natural samples. As already evidenced when measuring labelled water, it calls for consideration of the compositions of several previous samples to obtain an appropriate correction, a prerequisite to achieve high‐precision data. [ABSTRACT FROM AUTHOR]

The gas-phase kinetics of phenyl radical (·C6H5) with ethyl formate (HCO2Et, EF) was investigated experimentally using ultrasensitive laser-based cavity ring-down spectroscopy (CRDS). Phenyl radicals were generated by photolyzing nitrosobenzene (C6H5NO) at 248 nm and thereby probed at 504.8 nm. The rate coefficients for the (phenyl radical + EF) reaction were investigated between the temperatures of 260 and 361 K and at a pressure of 61 Torr with nitrogen (N2) as diluent. The temperature-dependent Arrhenius expression for the test reaction was obtained as: k phenyl + EF Expt , 260 - 361 K =(1.20 ± 0.16) × 10–13 exp[−(435.6 ± 50.0)/T] cm3 molecule−1 s−1 and the rate coefficient at room temperature was measured out to be: k phenyl + EF Expt , 298 K =(4.54 ± 0.42) × 10–14 cm3 molecule−1 s−1. The effects of pressure and laser fluence on the kinetics of the test reaction were found to be negligible within the experimental uncertainties. To complement the experimental findings, kinetics for the reaction of phenyl radicals with EF was investigated theoretically using Canonical Variational Transition State Theory (CVT) with Small Curvature Tunnelling (SCT) at CCSD(T)/cc-pVDZ//B3LYP/6–31 + G(d,p) level of theory in the temperatures between 200 and 400 K. The theoretically calculated rate coefficients for the title reaction were expressed in the Arrhenius form as: k phenyl + EF Theory , 200 - 400 K = (1.48 ± 0.56) × 10–38 × T8.47 × exp[(2431.3 ± 322.0)/T] cm3 molecule−1 s−1 and the corresponding rate coefficient at room temperature was calculated to be: k phenyl + EF Theory , 298 K = 4.91 × 10–14 cm3 molecule−1 s−1. A very good agreement was observed between the experimentally measured and theoretically calculated rate coefficients at 298 K. Thermochemical parameters as well as branching ratios for the reaction of (phenyl radical + EF) are also discussed in this manuscript. [ABSTRACT FROM AUTHOR]

Water stable isotopes have been widely used as natural tracers to investigate soil–plant–atmosphere interactions. Recent developments in induction module cavity ring-down spectroscopy (IM-CRDS) have made it possible to rapidly complete isotope analyses, and to combust co-extracted organic compounds at the same time. However, the agreement between IM-CRDS and isotope ratio mass spectrometry (IRMS) analyses has generally been poor and was primarily attributable to spectral interference of IM-CRDS. Here we evaluated the impacts of organic contamination on the isotope ratios using IM-CRDS with two different methods. No spectral interference was observed for solid samples measured directly by IM-CRDS, whereas clear organic contamination occurred in isotope analyses for pre-extracted plant stem and leaf samples. Our results demonstrate that IM-CRDS can fully combust co-extracted organic compounds by in-line oxidation in the direct measurement of solid samples, although this may not guarantee that the IM-CRDS can obtain better isotopic data than IRMS. It may be risky to evaluate the performance of IM-CRDS by measuring pre-extracted water samples because cryogenic vacuum distillation is likely to introduce extra organic compounds, which may not be fully removed during subsequent IM-CRDS measurement. In addition, spectral variables are useful for post-processing corrections. [ABSTRACT FROM AUTHOR]

We present measurements of isoprene-derived organic nitrates (ISOP-NITs) generated in the reaction of isoprene with the nitrate radical (NO3) in a 1 m³ Teflon reaction chamber. Detection of ISOP-NITs is achieved via their thermal dissociation to nitrogen dioxide (NO2), which is monitored by cavity ring-down spectroscopy (TD-CRDS). Using thermal dissociation inlets (TDIs) made of quartz, the temperature-dependent dissociation profiles (thermograms) of ISOP-NITs measured in the presence of ozone (O3) are broad (350 to 700 K), which contrasts the narrower profiles previously observed for e.g. isopropyl nitrate (iPN) or peroxy acetyl nitrate (PAN) under the same conditions. The shape of the thermograms varied with the TDI's surface to volume ratio and with material of the inlet walls, providing clear evidence that ozone and quartz surfaces catalyse the dissociation of unsaturated organic nitrates leading to formation of NO2 at temperatures well below 475 K, impeding the separate detection of alkyl nitrates (ANs) and peroxy nitrates (PNs). We present a simple, viable solution to this problem and discuss the potential for interference by the thermolysis of nitric acid (HNO3), nitrous acid (HONO) and O3. [ABSTRACT FROM AUTHOR]