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Explosives and explosive-related compounds usually have dissociative excited electronic states. We consider the effect of excited-state dissociation upon an absorption event on the UV cavity ringdown spectroscopy (CRDS) detection of these molecules. A change in the photon decay lifetime with increasing laser energy is demonstrated with vapors of 2,6-dinitrotoluene in the open atmosphere. The magnitude of the effect is modeled with coupled equations describing the time-dependent light intensity and molecular concentration within the cavity. The light intensities required within this model to explain the observed changes in the photon decay lifetimes are consistent with the light intensities expected within the cavity under our experimental conditions. It was also found that the slow diffusion of the molecules in static air can magnify the effect of photochemistry on UV CRDS trace detection of molecules with dissociative excited states. OCIS codes: 280.3420, 300.1030, 300.6390.

Determination of OH number sensities outside of a platinum catalyst using cavity ringdown spectroscopy was carried out. The relative concentration of OH probed with LIF appeared to be lower compared that determined by CRDS which might be due to electron quenching as indicated by a shorter fluorescence lifetime.

The first use of cavity ringdown spectroscopy (CRDS) to measure differential (angular) sputter yield profiles of sputtered particles is reported. Owing to the path-integrated nature of CRDS, inversion techniques are required. Our approach is to scan the optical axis relative to the source of sputtered particles and to measure the spatial profile of the CRDS signals. Modeling is then used to determine the differential sputter yield profile from the measured CRDS spatial profile. Demonstrative measurements are made with a Nd:YAG pumped optical parametric oscillator laser system for 750 eV argon ions normally incident on a molybdenum target. At these conditions we find an under-cosine sputtering distribution characterized by a = 0.22 [+ or -] 0.07 in good agreement with past quartz crystal microbalance measurements (a = 0.19). OCIS codes: 300.1030, 120.4290, 120.6780.

The detection of vapors of dinitrobenzenes and dinitrotoluenes by UV cavity ringdown spectroscopy (CRDS) was investigated. Absorption cross sections at 248 nm were estimated by measurements on saturated vapors and compared with solution-phase values. The computed subparts per [10.sup.9] detection sensitivity with no effort at preconcentration was demonstrated through measurements on diluted flows. The factors affecting measurements on 1 atm total pressure were considered, and it was demonstrated that Rayleigh scattering by air will reduce the detection sensitivity by 5%-10%. The UV absorption spectra of these compounds are broad, resulting in a relatively poor selectivity for single-wavelength measurements with the UV CRDS technique. OCIS codes: 280.3420, 300.1030, 300.6390.

We present the high resolution infrared detection of fifteen highly vibrationally excited nν1 + mν3 combination bands (n ≤ 7 and m ≤ 3) of C3 produced in a supersonically expanding propyne plasma, of which fourteen are reported for the first time. The fully resolved spectrum, around 3 μm, is recorded using continuous wave cavity ring-down spectroscopy. A detailed analysis of the resulting spectra is provided by ro-vibrational calculations based on an accurate local ab initio potential energy surface for C3 ( X ̃ 1 Σ g + ). The experimental results not only offer a significant extension of the available data set, extending the observed number of quanta v 1 to 7 and v 3 to 3, but also a vital test to the fundamental understanding of this benchmark molecule. The present variational calculations give remarkable agreement compared to experimental values with typical accuracies of ∼0.01% for the vibrational frequencies and ∼0.001% for the rotational parameters, even for high energy levels around 10 000 cm−1. [ABSTRACT FROM AUTHOR]

Stable water isotope measurements from polar ice cores provide high-resolution information about past hydrologic conditions and are therefore important for understanding earth's climate system. Routine high-resolution measurements of δ18 O, δ D, and deuterium excess are made by continuous-flow analysis (CFA) methods that include laser spectrometers. Cavity ring-down laser spectroscopy (CRDS) allows for simultaneous measurements of all stable water isotopes, including δ17 O and 17 O excess (Δ17 O); however, the limitations of CFA methodologies for Δ17 O are not well understood. Here, we describe a measurement methodology for all stable water isotopes that uses a CFA system coupled with a CRDS instrument. We make repeated measurements of an ice-core section using this method to explore the reproducibility of CFA–CRDS measurements for Δ17 O. Our data demonstrate that the CFA–CRDS method can make high-precision measurements of Δ17 O (< 5 per meg at averaging times > 3000 s). We show that the variations within our CFA ice-core measurements are well matched in magnitude and timing by the variations within the discrete CRDS measurements; we find that calibration offsets generate most of the variability among the replicate datasets. When these offsets are accounted for, the precision of CFA–CRDS ice-core data for Δ17 O is as good as the precision of Δ17 O for continuous reference water measurements. We demonstrate that this method can detect seasonal variability in Δ17 O in Greenland ice, and our work suggests that the measurement resolution of CFA–CRDS is largely defined by the melt and measurement rate. We suggest that CFA–CRDS has the potential to increase measurement resolution of δ17 O and Δ17 O in ice cores, but also highlight the importance of developing calibration strategies with attention to Δ17 O. [ABSTRACT FROM AUTHOR]

Water vapor absorption in the near-ultraviolet region is essential to describe the energy budget of Earth, but little spectroscopic information is available since it is a challenging spectral region for both experimental and theoretical studies. A continuous-wave cavity ring-down spectroscopic experiment was built to record absorption lines of water vapor around 415 nm. With a precision of 4×10-10 cm -1 , 40 rovibrational transitions of H 216 O were observed in this work, and 27 of them were assigned to the (224), (205), (710), (304), (093), (125) and (531) vibrational bands. A comparison of line positions and intensities determined in this work to the most recent HITRAN database is presented. Water vapor absorption cross-sections near 415 nm were calculated based on our measurements, which vary between 1×10-26 and 5×10-26 cm 2 molec. -1. These data will also significantly impact the spectroscopy detection of trace gas species in the near-UV region. [ABSTRACT FROM AUTHOR]

A sensitive, compact detector for the simultaneous measurement of O3 and NO2 is presented in this work. There are two channels in the detector, namely the Ox channel and the NO2 channel. In the presence of excess NO, ambient O3 is converted to NO2 in the Ox measurement channel. In both channels, NO2 is directly detected via cavity ring-down spectroscopy (CRDS) at 409 nm. At a 10 s integration time, the Ox and NO2 channels have a 1σ precision of 14.5 and 13.5 pptv, respectively. The Allan deviation plot shows that the optimal sensitivity of O3 and NO2 occurs at an integration time of ~60 s, with values of 10.2 and 8.5 pptv, respectively. The accuracy is 6% for the O3 channel and 5% for the NO2 channel, and the largest uncertainty comes from the effective NO2 absorption cross-section. Intercomparison of the NO2 detection between the NO2 and Ox channels shows good agreement within their uncertainties, with an absolute shift of 0.31 ppbv, a correlation coefficient of R2 = 0.99 and a slope of 0.98. Further intercomparison for ambient O3 measurement between the O3/NO2-CRDS developed in this work and a commercial UV O3 monitor also shows excellent agreement, with linear regression slopes close to unity and an R2 value of 0.99 for 1 min averaged data. The system was deployed to measure O3 and NO2 concentrations in Hefei, China, and the observation results show obvious diurnal variation characteristics. The successful deployment of the system has demonstrated that the instrument can provide a new method for retrieving fast variations in ambient O3 and NO2. [ABSTRACT FROM AUTHOR]

The cavity ringdown (CRD) absorption spectrum of 2-cyclohexen-1-one (2CHO) was recorded over the range 401.5-410.5 nm in a room-temperature gas cell. The very weak band system ([variant_greek_epsilon] <= 0.1 M-1 cm-1) in this spectral region is due to the T1(n, π*) ← S0 electronic transition. The 000 origin band was assigned to the feature observed at 24 558.8 ± 0.3 cm-1. We have assigned 46 vibronic transitions in a region extending from -200 to +350 cm-1 relative to the origin band. For the majority of these transitions, we have made corresponding assignments in the spectrum of the deuterated derivative 2CHO-2,6,6-d3. From the assignments, we determined fundamental frequencies for several vibrational modes in the T1(n, π*) excited state of 2CHO, including the lowest ring-twisting (99.6 cm-1) and ring-bending (262.2 cm-1) modes. These values compare to fundamentals of 122.2 cm-1 and 251.9 cm-1, respectively, determined previously for the isoconfigurational S1(n, π*) excited state of 2CHO and 99 cm-1 and 248 cm-1, respectively, for the S0 ground state. With the aid of quantum-mechanical calculations, we have also ascertained descriptions for these two modes, thereby resolving ambiguities appearing in the previous literature. The ring-twisting mode (ν39) contains a significant contribution from O=C-C=C torsion, whereas the ring-bending mode (ν38 in the ground state) involves mainly the motion of C-5 with respect to the plane containing the other heavy atoms. The CRD spectroscopic data for the T1(n, π*) state have allowed us to benchmark several computational methods for treating excited states, including time-dependent density functional theory and an equation-of-motion coupled cluster method. In turn, the computational results provide an explanation for observed differences in the T1(n, π*) vs. S1(n, π*) ring frequencies. [ABSTRACT FROM AUTHOR]

The near-infrared cavity ringdown spectroscopy (NIR CRDS) spectra of butyl peroxy isomers are described. NIR CRDS is capable of distinguishing not only different chemical species RO(sub 2) and R'O(sub 2) but also among different isomers, and even conformers, of a given RO(sub 2) radical.

Atmospheric nitrate radicals (N[O.sub.3]) are detected using off-axis cavity ringdown spectroscopy (CRDS) for the first time to our knowledge with a room-temperature continuous-wave (cw) diode laser operating near 662 nm. A prototype instrument was constructed that achieved a 1[sigma] absorption sensitivity of 5 x [10.sup.-10] [cm.sup.-1] [Hz.sup.-1/2], corresponding to a 1.4 part per trillion by volume 2[sigma] detection limit in 4.6 s at 80[degrees]C. This sensitivity is a significant improvement over a recent implementation of off-axis cavity-enhanced absorption spectroscopy and comparable to that of the most advanced cw CRDS and pulsed CRDS applications for atmospheric detection of N[O.sub.3]. A comparison of measurements of ambient air in Fairbanks, Alaska, recorded with the off-axis CRDS instrument and a previously characterized conventional cw CRDS instrument showed good agreement ([R.sup.2] = 0.97). OCIS codes: 010.1280, 300.1030.

The cavity ringdown spectra of the A-X electronic transitions of all eight isomers of the pentyl peroxy radicals are investigated. The relative reactivity of the primary, secondary and tertiary hydrogen atoms in isopentane is also determined semiquantitatively using the analyzed spectra.

The 4 H -pyran-4-one (4PN) molecule serves as a model for investigating structural changes following π* ← n electronic excitation. We have recorded the cavity ringdown (CRD) absorption spectrum of 4PN vapor at room temperature, over the wavelength region from 350 to 370 nm. This spectral region includes the T 1 (n,π*) ← S 0 band system as well as the low-energy portion of the S 1 (n,π*) ← S 0 system. Aided by predictions from ab initio (equation-of-motion excitation energies with dynamical correlation incorporated at the level of coupled cluster singles doubles, EOM-EE-CCSD) and density functional theory (time-dependent density functional theory with PBE0 functional, TDPBE0) calculations, we have made vibronic assignments for about 30 features in the CRD spectrum, mostly T 1 (n,π*) ← S 0 transitions. We have used these results to correct certain vibronic assignments appearing in the previous literature for both T 1 (n,π*) ← S 0 and S 1 (n,π*) ← S 0 band systems. We conclude that the lowest-energy carbonyl wagging fundamentals (ν 27 , in-plane and ν 17 , out-of-plane) undergo significant frequency drops (28 and 50%, respectively) upon T 1 (n,π*) ← S 0 excitation and similar drops (29 and 39%, respectively) for S 1 (n,π*) ← S 0 excitation. We find that vibrational modes involving the conjugated ring atoms undergo relatively small frequency changes upon π* ← n excitation, for both T 1 and S 1 states. We have used the present spectroscopic results and vibronic assignments to test the accuracy of computed excited-state frequencies for 4PN. This benchmarking process shows that the economical time-dependent density functional theory method is impressively accurate for certain (but not all) vibrational modes. The highly correlated EOM-EE-CCSD ab initio method is capable of making accurate frequency predictions, but the results, unexpectedly, depend sensitively on basis set family. This anomaly is traceable to a computed conical intersection between the T 1 (n,π*) and T 2 (π,π*) surfaces near the T 1 (n,π*) potential minimum. Relatively small errors in the location of the conical intersection lead to enhanced mixing of the two electronic states and incorrect T 1 (n,π*) vibrational frequencies when certain triple-ζ quality basis sets are used.

Optical extinction by homogeneous, pure water droplets of 30 to 70 [micro]m diameter produced by a vibrating orifice aerosol generator has been studied by pulsed cavity ringdown (CRD) spectroscopy at [lambda] = 560 nm under ambient conditions. Experimental sensitivity of better than 1% achieved in measurements of CRD times enabled detection of changes in laser light losses per pass due to changes in the number and size of particles within the laser beam volume. By systematically changing the droplet size in the cavity while recording the CRD time, a periodic modulation in the value of the loss per pass was observed. The modulation is caused by the oscillatory nature of the extinction efficiency, which was subsequently inferred and compared with the results of theoretical calculations based on Mie theory. [C] 2007 Optical Society of America OCIS codes: 010.1100, 010.1110, 010.1310, 290.4020, 300.6360.

We demonstrate a simple periodically locked cw cavity ringdown spectroscopy technique that enables a very large number of ringdown events to be rapidly acquired. An external cavity diode laser is locked to a high-finesse cavity, and as many as 16,000 ringdown events per second are obtained by periodically switching off the light entering the high-finesse cavity. Following each ringdown event, the light to the cavity is switched back on and cavity lock is rapidly reacquired. Limited only by our relatively modest digitization rate, we obtained a minimum detectable absorption loss of 4.7 x [10.sup.-9] [cm.sup.-1], but we show that faster digitization could provide a sensitivity of 5.9 x [10.sup.-10] [cm.sup.-1] [Hz.sup.-1/2]. OCIS codes: 020.0020, 120.0120, 140.2020, 300.0300.

We have recorded high resolution, partially rotationally resolved, jet-cooled cavity ringdown spectra of the origin band of the Ã-X electronic transition of both the G and T conformers of the perproteo and perdeutero isotopologues of the ethyl peroxy radical, C2H5O2. This transition, located in the near infrared, was studied using a narrow band laser source (<=250 MHz) and a supersonic slit-jet expansion coupled with an electric discharge allowing us to obtain rotational temperatures of about 15 K. All four spectra have been successfully simulated using an evolutionary algorithm approach with a Hamiltonian including rotational and spin-rotational terms. Excellent agreement with the experimental spectra was obtained by fitting seven molecular parameters in each ground and the first excited electronic states as well as the band origin of the electronic transition. This analysis unambiguously confirms the assignment of the lower frequency origin band to the G conformer and the higher frequency one to the T conformer. [ABSTRACT FROM AUTHOR]

State-of-the-art experiments and calculations are used to record and assign the data obtained in the weakly absorbing blue energy region of the H2O spectrum. Continuous-wave cavity ringdown absorption spectroscopy with Doppler resolution is used to probe the range from 25 195 to 25 470 cm-1 with an absorption sensitivity of ∼1 parts per 109 (ppb)/cm. 62 lines of the polyad νOH=8 are reported, of which 43 are assigned using variational nuclear calculations. The study includes absorption line intensities (in the range of 10-28–10-26 cm/molecule) for all lines and self-broadening pressure coefficient for a few lines. The newly obtained energy levels are also reported. [ABSTRACT FROM AUTHOR]

We report the design and performance of a tunable, pulsed high resolution mid infrared cavity ringdown spectrometer. Stimulated Raman scattering in H[sub 2]/D[sub 2] is used to downconvert the output of a SLM Alexandrite ring laser (720–800 nm) to the mid infrared (3–8 μm). The infrared frequency bandwidth was determined to be 90±5 MHz from measurements of Doppler broadened OCS transitions at 5 μm. The minimum detectable per pass fractional absorption is 1 ppm. We observe a frequency dependent ringdown cavity transmission of ±5 ppm due to spatial variations of the mirror reflectivity. The υ[sub 6] band of linear C[sub 9] formed by laser ablation of graphite in a He molecular beam was measured, showing a factor of 2 improvement in sensitivity relative to previous IR diode laser experiments. Based on calculated IR intensities, the number density of C[sub 9] in the molecular beam is 1.3[sup *]10[sup 11] molec/cm[sup 3] and the minimum detectable density is 1[sup *]10[sup 9] molec/cm[sup 3]. We expect this spectrometer to be a powerful tool for the study of transient species formed in molecular beams. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Mitigation of greenhouse gases requires a precise knowledge of their sources at both global and regional scales. With improving measurement techniques, in situ δ(13C,CH4) records are analysed in a growing number of studies to characterise methane emissions and to evaluate inventories at regional and local scales. However, most of these studies cover short time periods of a few months, and the results show a large regional variability. In this study, a 6-year time record of in situ δ(13C,CH4) , measured with a cavity ring-down spectroscopy (CRDS) analyser in Heidelberg, Germany, is analysed to obtain information about seasonal variations and trends of CH 4 emissions. The Keeling plot method is applied to atmospheric measurements on different timescales, and the resulting source contributions are used to evaluate the CH 4 emissions reported by two emission inventories: the Emissions Database for Global Atmospheric Research (EDGAR v6.0) and the inventory of the State Institute for the Environment Baden-Württemberg (LUBW). The mean isotopic carbon source signature for the Heidelberg catchment area derived from atmospheric measurements is (-52.3±0.4) ‰ and shows an annual cycle with 5.8 ‰ more depleted values in summer than in winter. This annual cycle can only be partly explained by seasonal variations in the 13 C-enriched emissions from heating and reveals strong seasonal variations in biogenic CH 4 emissions in the Heidelberg catchment area, which are not included in EDGAR v6.0. The comparison with emission inventories also shows that EDGAR v6.0 overestimates the CH 4 emissions from less depleted sources. In situ CH 4 isotope analysers at continental and urban monitoring stations can make an important contribution to the verification and improvement of emission inventories. [ABSTRACT FROM AUTHOR]

Rationale: The presence of substantial amounts of dissolved salts creates serious difficulties in isotope analyses of water samples using conventional isotope ratio mass spectrometry. Although nowadays laser‐based instruments are increasingly used for this purpose, a comprehensive assessment of isotope effects associated with direct analyses of aqueous saline solutions using this technology is lacking. Methods: Here we report the results of laboratory experiments aimed at quantifying isotope effects associated with direct, δ2H, δ18O and δ17O analyses of single‐salt solutions and double‐salt mixtures prepared with a water of known isotopic composition. Three single‐salt solutions (NaCl, CaCl2 and MgSO4) and two double‐salt mixtures (NaCl + CaCl2 and NaCl + MgSO4) were prepared and investigated for a wide range of molalities. The triple‐isotope composition of the prepared solutions was analysed with the aid of a Picarro L2140‐i Cavity Ring‐Down Spectroscopy analyser. Results: The NaCl and CaCl2 solutions revealed small negative salt effects, independent of molality and comparable with measurement uncertainty. The MgCl2 solution showed the highest salt effects, reaching saturated solution ca. +2.7‰ (2H), −3.5‰ (18O) and −1.7‰ (17O). Salt effects for the double‐salt mixtures generally mirrored the effects observed for the single‐salt solutions. The observed salt effects are discussed in the context of processes occurring during the injection of the salt solutions into the vaporizer unit of the CRDS analyser. Conclusions: The presented study has demonstrated feasibility of direct, triple‐isotope analyses of aqueous salt solutions using a Picarro L2140‐i CRDS analyser for a broad range of salinities up to saturated conditions. Large uncertainties of 17O‐excess determinations for solutions forming hydrated salts preclude the use of this parameter for interpretation purposes. [ABSTRACT FROM AUTHOR]

We present a high-resolution study on the B2Π-X2Π electronic origin band spectrum of the C6H radical with its center at ~18990 cm-1 The C6H radicals are produced in a pulsed supersonic slit-jet discharge source and detected in direct absorption by sensitive cavity ring-down spectroscopy. By using a home-made narrow linewidth nanosecond pulsed laser source, the experimental spectrum allows to resolve the ∧-type doublet fine structures in high-J rotational lines. A set of improved B2Π state constants, including the ∧-type doubling parameters of p′ = −1.16(9)x10−3 cm−1q′ = -1.22(7)x10−4 cm−1 are determined from analysis of the experimental spectrum. An analysis on the spectral line profile has resulted in a significant linewidth broadening of ~0.05±0.01 cm−1, corresponding to a B2Π state lifetime of ~100±20 ps. The short lifetime of the excited B2Π state is proposed due to fast internal vibronic couplings to high-lying vibronic levels of lower electronic states. [ABSTRACT FROM AUTHOR]

We present the saturated absorption spectroscopy of the 30012←00001 band of 12C16O2 by a comb-locked cavity ring-down spectrometer near 1.57 µm. Positions of 37 lines with rotational quantum numbers up to 68 were determined with an accuracy of a few kHz. Comparisons of the ro-vibrational energy levels determined in this work with the Doppler-limited experimental values from literature and those from the CDSD2019 databank are given. Deviations exceeding 1 MHz were observed in the transitions blended by other carbon dioxide isotopologues. [ABSTRACT FROM AUTHOR]

Rationale: Soil microbial heterotrophic C‐CO2 respiration is important for C cycling. Soil CO2 differentiation and quantification are vital for understanding soil C cycling and CO2 emission mitigation. Presently, soil microbial respiration (SR) quantification models are based on native soil organic matter (SOM) and require consistent monitoring of δ13C and CO2. Methods: We present a new apparatus for achieving in situ soil static chamber incubation and simultaneous CO2 and δ13C monitoring by cavity ring‐down spectroscopy (CRDS) coupled with a soil culture and gas introduction module (SCGIM) with multi‐channel. After a meticulous five‐point inter‐calibration, the repeatability of CO2 and δ13C values by using CRDS‐SCGIM were determined, and compared with those obtained using gas chromatography (GC) and isotope ratio mass spectrometry (IRMS), respectively. We examined the method regarding quantifying SR with various concentrations and enrichment of glucose and then applied it to investigate the responses of SR to the addition of different exogenous organic materials (glucose and rice residues) into paddy soils during a 21‐day incubation. Results: The CRDS‐SCGIM CO2 and δ13C measurements were conducted with high precision (< 1.0 µmol/mol and 1‰, respectively). The optimal sampling interval and the amount added were not exceeded 4 h and 200 mg C/100 g dry soil in a 1 L incubation bottle, respectively; the 13C‐enrichment of 3%–7% was appropriate. The total SR rates observed were 0.6–4.2 µL/h/g and the exogenous organic materials induced ‐49%–28% of priming effects in native SOM mineralisation. Conclusions: Our results show that CRDS‐SCGIM is a method suitable for the quantification of soil microbial CO2 respiration, requiring less extensive lab resources than GC/IRMS. [ABSTRACT FROM AUTHOR]