Search

Cool red giant stars exhibit absorption bands of calcium monochloride (CaCl) in the optical region. In this work, the bands of CaCl corresponding to the A2Π − X2Σ+ transition with v ′ ≤ 4 and v ″ ≤ 4, and B2Σ+ − X2Σ+ transition with v ′ ≤ 2 and v ″ ≤ 2 are rotationally analyzed with PGOPHER, a multipurpose program for simulating and fitting molecular spectra. All bands were analyzed using high-resolution absorption spectra collected at the National Solar Observatory in 1985, calibrated with atomic lines from a high-resolution emission spectrum obtained in a separate hollow cathode experiment. The results are compared with previous laser-induced fluorescence measurements. Overall, the accuracy of spectroscopic constants for the A2Π and B2Σ+ states is improved. Scaled transition dipole moment calculations were used to obtain line strengths. Line lists are provided with Einstein A coefficients and oscillator strengths, which can be used to determine CaCl stellar abundances. Additionally, isotope splittings allowed us to estimate band origins for the 40Ca37Cl isotopologue based on band-head positions. [ABSTRACT FROM AUTHOR]

We report and interpret recently recorded high-resolution infrared spectra for the fundamentals of the CH2 scissors and CH stretches of gas phase cyclopentane at −26.1 and −50 °C, respectively. We extend previous theoretical studies of this molecule, which is known to undergo barrierless pseudorotation due to ring puckering, by constructing local mode Hamiltonians of the stretching and scissor vibrations for which the frequencies, couplings, and linear dipoles are calculated as functions of the pseudorotation angle using B3LYP/6-311++(d,p) and MP2/cc-pVTZ levels of theory. Symmetrization (D5h) of the vibrational basis sets leads to simple vibration/pseudorotation Hamiltonians whose solutions lead to good agreement with the experiment at medium resolution, but which miss interesting line fractionation when compared to the high-resolution spectra. In contrast to the scissor motion, pseudorotation leads to significant state mixing of the CH stretches, which themselves are Fermi coupled to the scissor overtones. [ABSTRACT FROM AUTHOR]

The ZrO B 1Π– X 1Σ+, B 1Π– A 1Δ, and C 1Σ+– X 1Σ+ band systems are important opacity sources in the near-infrared and optical spectra of S-type stars. A total of 21 rovibronic bands with v ″ ≤ 7 and v ′ ≤ 5 were observed and fit for the B 1Π– X 1Σ+ transition, five bands for the 90ZrO B 1Π– A 1Δ transition and one band for the 90ZrO C 1Σ+– X 1Σ+ transition. All band systems were analyzed using high-temperature, high-resolution emission spectra collected at the National Solar Observatory (Kitt Peak). A modern spectroscopic analysis was performed using the PGOPHER program to provide updated spectroscopic constants. In general, we improve the accuracy of the line positions reported in the literature and slightly extend the vibrational analysis. Equilibrium molecular constants were then derived and combined with new ab initio calculations of transition dipole moment functions to produce line lists with line strengths. [ABSTRACT FROM AUTHOR]

Infrared aerosol spectra derived from Atmospheric Chemistry Experiment measurements following the June 2019 Raikoke volcanic eruption are used to evaluate the composition of stratospheric aerosols in the Arctic. A blanket of aerosols, spanning an altitude range from the tropopause (8–11 km) to 20 km, persisted in the stratosphere over northern latitudes for many months. The aerosols within this blanket were almost exclusively sulfates. The percentage of sulfuric acid in the aerosols decreased over time, dropping below 50% H2SO4 concentration at some altitudes by March 2020. Contrary to previous reports, the aerosol blanket was not comprised of smoke particles. Plain Language Summary: Particles in the atmosphere were measured from a satellite‐based instrument following the 2019 eruption of the Raikoke volcano. These particles were found to be predominately liquid droplets containing a mixture of sulfuric acid and water. A thick blanket of the particles settled over northern regions and lasted for months. Contrary to previous reports, particles in this blanket did not consist of smoke from intense fires that occurred shortly after the volcano's eruption. Key Points: Following the Raikoke eruption, a layer of sulfate aerosols developed in the stratosphere over northern latitudes, persisting for monthsAerosol composition and physical properties were derived from measurements by the Atmospheric Chemistry ExperimentNo evidence of stratospheric smoke was found in the Arctic region, contradicting previous reports [ABSTRACT FROM AUTHOR]

Thirteen bands for the B¹Δg-A¹Πu system and eleven bands for the B'¹Σg+-A¹Πu system of C2 were identified in the Fourier transform infrared emission spectra of hydrocarbon discharges. The B'¹Σg+ v = 4 and the B¹Δg v = 6, 7, and 8 vibrational levels involved in nine bands were studied for the first time. A direct global analysis with Dunham parameters was carried out satisfactorily for the B¹Δg-A¹Πu system except for a small perturbation in the B¹Δg v = 6 level. The calculated rovibrational term energies up to B¹Δg v = 12 showed that the level crossing between the B¹Δg and d³Πg states is responsible for many of the prominent perturbations in the Swan system observed previously. Nineteen forbidden transitions of the B¹Δg-a3?u transition were identified and the off-diagonal spin-orbit interaction constant AdB between d³Πg and B¹Δg was derived as 8.3(1) cm-1. For the B'¹Σg+-A¹Πu system, only individual band analyses for each vibrational level in the B'¹Σg+ state could be done satisfactorily and Dunham parameters obtained from these effective parameters showed that the anharmonic vibrational constant wexe is anomalously small (nearly zero). Inspection of the RKR (Rydberg-Klein-Rees) potential curves for the B'¹Σg+ and X¹Σg+ states revealed that an avoided crossing or nearly avoided crossing may occur around 30 000 cm-1, which is responsible for the anomalous molecular constants in these two states. [ABSTRACT FROM AUTHOR]

6229 lines of the Ballik-Ramsay system (b³Σg--a³Πu) and the Phillips system (A¹Πu -X¹Σg+) of C2 up to v = 8 and J = 76, which were taken from the literature or assigned in the present work, were analyzed simultaneously by least-squares fitting with 82 Dunham-like molecular parameters and spin-orbit interaction constants between the b³Σg- and X¹Σg+ states with a standard deviation of 0.0037 cm-1 for the whole data set. As a result of the deperturbation analysis, the spin-orbit interaction constant AbX was determined as 6.333(7) cm-1 and the energy difference between the X¹Σg+ and a 3Πu states was determined as 720.008(2) cm-1 for the potential minima or 613.650(3) cm-1 for the v = 0 levels with Merer and Brown's N² Hamiltonian for ³Π states, which is about 3.3 cm-1 larger than the previously determined value. Due to this sizable change, a new energy-level crossing was found at J = 2 for v = 3 (F1) of b³Σg- state and v = 6 of X¹Σg+ state, where the strong interaction causes a nearly complete mixing of the wave functions of the b³Σg- and X¹Σg+ states and the forbidden transitions become observable. Using the predictions of our deperturbation analysis, we were able to identify 16 forbidden transitions between the singlet and triplet states at the predicted frequencies with the expected intensities, which verifies our value for the energy difference between the X¹Σg+ and a³Πu states. [ABSTRACT FROM AUTHOR]

The phase out of anthropogenic ozone‐depleting substances such as chlorofluorocarbons under the terms of the Montreal Protocol led to the development and worldwide use of hydrofluorocarbons (HFCs) in refrigeration, air conditioning, and as blowing agents and propellants. Consequently, over recent years, the atmospheric abundances of HFCs have dramatically increased. HFCs are powerful greenhouse gases and are now controlled under the terms of the 2016 Kigali Amendment to the Montreal Protocol. HFC‐134a is currently the most abundant HFC in the atmosphere, breaking the 100 ppt barrier in 2018, and can be measured in the Earth's atmosphere by the satellite remote‐sensing instrument ACE‐FTS (Atmospheric Chemistry Experiment‐Fourier Transform Spectrometer), which has been measuring since 2004. This work uses the ACE‐FTS v4.0 data product to investigate global distributions and trends of HFC‐134a. These measurements are compared with a simulation of SLIMCAT, a state‐of‐the‐art three‐dimensional chemical transport model, which is constrained by global surface HFC‐134a measurements. The agreement between observation and model is good, although in the tropical troposphere ACE‐FTS measurements are biased low by up to 10–15 ppt. The overall ACE‐FTS global trend of HFC‐134a for the altitude range 5.5–24.5 km and 2004–2018 time period is approximately linear with a value of 4.49 ± 0.02 ppt/year, slightly lower than the corresponding SLIMCAT trend of 4.66 ppt/year. Using a simple box model, we also estimate the annual global emissions and burdens of HFC‐134a from the model data, indicating that emissions of HFC‐134a have increased almost linearly, reaching 236 Gg by 2018. Key Points: First comparison between long‐term satellite measurements (ACE‐FTS) of atmospheric HFC‐134a and a 3D chemical transport model (SLIMCAT)Observations agree well with SLIMCAT, although ACE‐FTS is biased low by up to 10–15 ppt in the troposphere between 30°S and 30°NGlobal trends are linear to a good approximation: 4.49 ppt/year for ACE‐FTS (2004–2018; 5.5–24.5 km) and 4.66 ppt/year for SLIMCAT [ABSTRACT FROM AUTHOR]

A new line list for rovibrational and rotational transitions, including fine structure, within the NH X³Σ - ground state has been created. It contains line intensities in the form of Einstein A and fvalues, for all possible bands up to v' = 6, and for J up to between 25 and 44. The intensities are based on a new dipole moment function (DMF), which has been calculated using the internally contracted multi-reference configuration interaction method with an aug-cc-pV6Z basis set. The programs RKR1, LEVEL, and PGOPHER were used to calculate line positions and intensities using the most recent spectroscopic line position observations and the new DMF, including the rotational dependence on the matrix elements. The Hund's case (b) matrix elements from the LEVEL output (available as Supplement 1 of the supplementary material) have been transformed to the case (a) form required by PGOPHER. New relative intensities for the (1,0) band have been measured, and the calculated and observed Herman-Wallis effects are compared, showing good agreement. The line list (see Supplement 5 of the supplementary material) will be useful for the study of NH in astronomy, cold and ultracold molecular systems, and in the nitrogen chemistry of combustion. [ABSTRACT FROM AUTHOR]

Deperturbation analysis of the A 2Π → X 2Σ+ and B′ 2Σ+ → X 2Σ+ emission spectra of 24MgH is reported. Spectroscopic data for the v = 0 to 3 levels of the A 2Π state and the v = 0 to 4 levels of the B′ 2Σ+ state were fitted together using a single Hamiltonian matrix that includes 2Π and 2Σ+ matrix elements, as well as off-diagonal elements coupling several vibrational levels of the two states. A Dunham-type fit was performed and the resulting Yl,0 and Yl,1 coefficients were used to generate Rydberg-Klein-Rees (RKR) potential curves for the A 2Π and the B′ 2Σ+ states. Vibrational overlap integrals were computed from the RKR potentials, and the off-diagonal matrix elements coupling the electronic wavefunctions (a+ and b) were determined. Zero point dissociation energies (D0) of the A 2Π and B′ 2Σ+ states of 24MgH were determined to be 12 957.5 ± 0.5 and 10 133.6 ± 0.5 cm-1, respectively. Using the Y0,1 coefficients, the equilibrium internuclear distances (re) of the A 2Π and B′ 2Σ+ states were determined to be 1.67827(1) Å and 2.59404(4) Å, respectively. [ABSTRACT FROM AUTHOR]

New high-resolution infrared and UV/visible spectra of 107AgH, 109AgH, 107AgD, and 109AgD have been recorded with a Fourier transform spectrometer. The new line positions are combined with published microwave and older electronic A 1Σ+-X 1Σ+ data and used, first in a decoupled analysis of the X state alone, and then in a global multi-isotopologue analysis which yields comprehensive descriptions of both the X 1Σ+ and A 1Σ+ states of all four isotopologues of AgH. While the A state was long believed to be heavily perturbed, it is shown that its irregular spectrum merely reflects an unusual potential function shape. A direct fit of all data to appropriate radial Hamiltonians yields analytic potential-energy functions and Born-Oppenheimer breakdown radial functions for the ground X 1Σ+ and A 1Σ+ states. [ABSTRACT FROM AUTHOR]

The high-resolution infrared emission spectrum of BeF2 vapor at 1000 °C was rotationally analyzed with the assistance of large-scale ab initio calculations using the coupled-cluster method including single and double excitations and perturbative inclusion of triple excitations, in conjunction with correlation-consistent basis sets up to quintuple-zeta quality. The ν3 fundamental band, the ν1+ν2, ν1+ν3, and 2ν2+ν3 combination bands, and 18 hot bands were assigned. The symmetric stretching (ν1), bending (ν2), and antisymmetric stretching (ν3) mode frequencies were determined to be 769.0943(2), 342.6145(3), and 1555.0480(1) cm-1, respectively, from the band origins of the ν3, ν1+ν3, and ν1+ν2 bands. The observed vibrational term values and B rotational constants were fitted simultaneously to an effective Hamiltonian model with Fermi resonance taken into account, and deperturbed equilibrium vibrational and rotational constants were obtained for BeF2. The equilibrium rotational constant (Be) was determined to be 0.235 354(41) cm-1, and the associated equilibrium bond distance (re) is 1.3730(1) Å. The results of our ab initio calculations are in remarkably good agreement with those of our experiment, and the calculated value was 1.374 Å for the equilibrium bond distance (re). As in the isoelectronic CO2 molecule, the Fermi resonance in BeF2 is very strong, and the interaction constant k122 was found to be 90.20(4) cm-1. [ABSTRACT FROM AUTHOR]

The vibration-rotation emission spectra of CdH2 and CdD2 molecules have been recorded at high resolution using a Fourier-transform spectrometer. The molecules were generated in a furnace-discharge emission source by reaction of cadmium vapor with molecular hydrogen or deuterium. The fundamental bands for the antisymmetric stretching mode (υ3) of CdH2 and CdD2 were detected at about 1771.5 and 1278.3 cm-1, respectively. In addition, the 002(Σg+)–001(Σu+) and 011(Πg)–010(Πu) hot bands were observed for CdH2. Spectroscopic constants were determined for each of the 12 observed isotopologs: 110CdH2, 111CdH2, 112CdH2, 113CdH2, 114CdH2, 116CdH2, 110CdD2, 111CdD2, 112CdD2, 113CdD2, 114CdD2, and 116CdD2. The average Cd-H and Cd-D bond distances (r0) were determined to be 1.683028(10) and 1.679161(16) Å, respectively. [ABSTRACT FROM AUTHOR]

An emission spectrum of hot water with a temperature of about 3000 K is obtained using an oxy-acetylene torch. This spectrum contains a very large number of transitions. The spectrum, along with previous cooler laboratory emission spectra and an absorption spectrum recorded from a sunspot, is analyzed in the 500–2000 cm-1 region. Use of a calculated variational linelist for water allows significant progress to be made on assigning transitions involving highly excited vibrational and rotational states. In particular emission from rotationally excited states up to J=42 and vibrational levels with up to eight quanta of bending motion are assigned. [ABSTRACT FROM AUTHOR]

Fourier transform emission spectra of D[sub 2]O vapor were recorded at a temperature of 1500 °C in the wavenumber range 380–1880 cm[sup -1]. 15 346 lines were measured, of which the majority were identified as belonging to D[sub 2]O. The spectrum was analyzed using variational nuclear motion calculations based on spectroscopically determined potential-energy surfaces. Initial assignments were made using a potential surface obtained by fitting a high accuracy ab initio potential. The new assignments were used to refine the potential surface, resulting in additional assignments. A total of 6400 D[sub 2]O transitions were assigned and 2144 new D[sub 2]O energy levels were obtained. Transitions involving the 4ν[sub 2] and 5ν[sub 2] bending states, with band origins of 4589.30 (±0.02) and 5679.6 (±0.1) cm[sup -1], respectively, were assigned for the first time.© 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

High resolution, near infrared emission spectra of TiH and TiD have been recorded with a Fourier transform spectrometer. The TiH and TiD molecules were made in a titanium hollow cathode lamp operated with a mixture of neon and hydrogen or deuterium gases. A heavily perturbed band system near 938 nm is assigned as a [sup 4]Φ-X[sup 4]Φ electronic transition. Line positions and approximate spectroscopic constants are reported for the 0-0 band of the new transition. The 4Φ-X[sup 4]Φ TiH transition might potentially be observed in late M-type stars and in L-type brown dwarfs. [ABSTRACT FROM AUTHOR]

Very short‐lived substances (VSLS), including dichloromethane (CH2Cl2), chloroform (CHCl3), perchloroethylene (C2Cl4), and 1,2‐dichloroethane (C2H4Cl2), are a stratospheric chlorine source and therefore contribute to ozone depletion. We quantify stratospheric chlorine trends from these VSLS (VSLCltot) using a chemical transport model and atmospheric measurements, including novel high‐altitude aircraft data from the NASA VIRGAS (2015) and POSIDON (2016) missions. We estimate VSLCltot increased from 69 (±14) parts per trillion (ppt) Cl in 2000 to 111 (±22) ppt Cl in 2017, with >80% delivered to the stratosphere through source gas injection, and the remainder from product gases. The modeled evolution of chlorine source gas injection agrees well with historical aircraft data, which corroborate reported surface CH2Cl2 increases since the mid‐2000s. The relative contribution of VSLS to total stratospheric chlorine increased from ~2% in 2000 to ~3.4% in 2017, reflecting both VSLS growth and decreases in long‐lived halocarbons. We derive a mean VSLCltot growth rate of 3.8 (±0.3) ppt Cl/year between 2004 and 2017, though year‐to‐year growth rates are variable and were small or negative in the period 2015–2017. Whether this is a transient effect, or longer‐term stabilization, requires monitoring. In the upper stratosphere, the modeled rate of HCl decline (2004–2017) is −5.2% per decade with VSLS included, in good agreement to ACE satellite data (−4.8% per decade), and 15% slower than a model simulation without VSLS. Thus, VSLS have offset a portion of stratospheric chlorine reductions since the mid‐2000s. Plain Language Summary: It is well established that long‐lived halogen‐containing compounds of anthropogenic origin, such as chlorofluorocarbons, have led to depletion of the stratospheric ozone layer. As production of these compounds is now controlled by the Montreal Protocol, the atmospheric abundance of chlorine/bromine is in decline, and the ozone layer should "recover" in coming decades. Here we consider the contribution of Very Short‐Lived Substances to stratospheric chlorine. These compounds also have anthropogenic sources, though are much less efficient at destroying ozone compared to, for example, most chlorofluorocarbons (per molecule emitted) as they break down more readily close to Earth's surface. Using surface observations and atmospheric model simulations, we show that stratospheric chlorine from short‐lived substances has increased since the early 2000s. This increase is also apparent from airborne measurements of their atmospheric abundance over the same period. Using the model in conjunction with satellite estimates of stratospheric chlorine, we show rising levels of short‐lived substances may be causing upper stratospheric chlorine to decline at a slower rate relative to what would be expected in their absence. While this offset in the rate of chlorine decline is modest (15%), it is nonnegligible and should be considered in the analysis of stratospheric composition trends. Key Points: Stratospheric chlorine from very short‐lived substances increased by 3.8 ppt/year over 2004–2017, with a growth slowdown in 2015–2017Chlorine from short‐lived substances improves model representation of upper stratospheric HCl trendsShort‐lived chlorine offsets the 2004–2017 rate of upper stratospheric HCl decline by 15% [ABSTRACT FROM AUTHOR]

Phosgene in the atmosphere is produced via the degradation of carbon tetrachloride, methyl chloroform, and a number of chlorine‐containing very short lived substances (VSLS). These VSLS are not regulated by the Montreal Protocol even though they contribute to stratospheric ozone depletion. While observations of VSLS can quantify direct stratospheric source gas injection, observations of phosgene in the upper troposphere/lower stratosphere can be used as a marker of product gas injection of chlorine‐containing VSLS. In this work we report upper troposphere/lower stratosphere measurements of phosgene made by the ACE‐FTS (Atmospheric Chemistry Experiment Fourier Transform Spectrometer) instrument and compare with results from the TOMCAT/SLIMCAT three‐dimensional chemical transport model to constrain phosgene trends over the 2004–2016 period. The 13‐year ACE‐FTS time series provides the first observational evidence for an increase in chlorine product gas injection. In 2016, VSLS accounted for 27% of modeled stratospheric phosgene, up from 20% in the mid‐2000s. Plain Language Summary: Atmospheric phosgene, a chlorine‐containing molecule, is produced via the degradation of the reasonably long lived species carbon tetrachloride and methyl chloroform, and a number of very short lived substances (VSLS), including dichloromethane, chloroform, and tetrachloroethene. Whereas the former are regulated by the Montreal Protocol because they contribute to stratospheric ozone depletion, these latter species are not. It is therefore important that we continue to monitor VSLS and the degradation products to determine how much additional chlorine, which catalyzes the destruction of ozone, is reaching the stratosphere. VSLS can either reach the stratosphere directly, via so‐called source gas injection, or degrade in the troposphere into products such as phosgene, which are then delivered into the stratosphere via so‐called product gas injection (PGI). Monitoring phosgene in the upper troposphere/lower stratosphere is therefore a marker for PGI due to chlorine‐containing VSLS. In this work we report measurements of phosgene in the upper troposphere/lower stratosphere made by the ACE‐FTS (Atmospheric Chemistry Experiment Fourier Transform Spectrometer) instrument. The 13‐year ACE‐FTS time series provides the first observational evidence for an increase in chlorine PGI, which has been predicted by atmospheric models. Key Points: A 13‐year global time series of phosgene in the upper troposphere/lower stratosphere is presented from ACE‐FTS dataThe observations provide evidence for an increase in phosgene in the upper troposphere and an overall decrease in the stratosphereThe increase in the upper troposphere is consistent with the increase in chlorine product gas injection predicted by a 3‐D model [ABSTRACT FROM AUTHOR]

We report here on the first high resolution infrared absorption spectra of the semistable nitrile oxide, NCCNO. All of the fundamental modes of vibration (except for the lowest-frequency bending mode) and several combination bands have been measured with a Fourier transform spectrometer at a resolution of 0.005 cm-1. In this paper, we present analyses of υ4, the C–C stretching mode at 714.753 94(6) cm-1, υ6, the NCC bending mode at 403.925 97(6) cm-1, υ6+υ7 at 490.123 62(6) cm-1, and the tentatively assigned υ5+υ6 combination band at 826.291 86(8) cm-1. A simultaneous least squares fit of these four bands gives ground state rotational constants of B0=0.077 085 54(34) cm-1 and D0=4.570(30)×10-9 cm-1. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The high-resolution infrared absorption spectrum of the oxalodinitrile di-N-oxide (ONCCNO) molecule has been recorded in the gas phase with a Fourier transform spectrometer at a resolution of 0.003 cm-1. No previous high-resolution spectra have been recorded for this semistable palindromic molecule. On the basis of the 2:1 intensity alternation in the rotational lines caused by nitrogen nuclear spin statistics, the ONCCNO molecule appears to be linear. A quasilinear structure, however, cannot be ruled out at this stage of the analysis. The ν4 and ν5 fundamental modes at 2246.040 55(23) cm-1 and 1258.475 30(11) cm-1 have been analyzed to give ground state rotational constants of B0=0.042 202 10(96) cm-1 and D0=8.77(70)×10-10 cm-1. By fixing the CN and NO bond lengths to 1.1923 and 1.1730 Å, respectively, the C–C bond length was determined to be 1.3329 Å using the B0 value. This short C–C bond length is thus similar to that observed for a carbon–carbon double bond. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

It is known from ground-based measurements made during the 1982-1983 and 1997-1998 El Niño events that atmospheric hydrogen cyanide (HCN) tends to be higher during such years than at other times. The Microwave Limb Sounder (MLS) on the Aura satellite has been measuring HCN mixing ratios since launch in 2004; the measurements are ongoing at the time of writing. The winter of 2015- 2016 saw the largest El Niño event since 1997-1998. We present MLS measurements of HCN in the lower stratosphere for the Aura mission to date, comparing the 2015- 2016 El Niño period to the rest of the mission. HCN in 2015- 2016 is higher than at any other time during the mission, but ground-based measurements suggest that it may have been even more elevated in 1997-1998. As the MLS HCN data are essentially unvalidated, we show them alongside data from the MIPAS and ACE-FTS instruments; the three instruments agree reasonably well in the tropical lower stratosphere. Global HCN emissions calculated from the Global Fire Emissions Database (GFED v4.1) database are much greater during large El Niño events and are greater in 1997- 1998 than in 2015-2016, thereby showing good qualitative agreement with the measurements. Correlation between El Niño-Southern Oscillation (ENSO) indices, measured HCN, and GFED HCN emissions is less clear if the 2015-2016 event is excluded. In particular, the 2009-2010 winter had fairly strong El Niño conditions and fairly large GFED HCN emissions, but very little effect is observed in the MLS HCN. [ABSTRACT FROM AUTHOR]

The distributions of the four most abundant isotopologues and isotopomers (N2O, 15NNO, N15NO, and NN18O) of nitrous oxide have been measured in the Earth's stratosphere by infrared remote sensing with the Atmospheric Chemistry Experiment (ACE) Fourier transform spectrometer. These satellite observations have provided a near-global picture of N2O isotopic fractionation. The relative abundances of the heavier species increase with altitude and with latitude in the stratosphere as the air becomes older. The heavy isotopologues are enriched by 20-30% in the upper stratosphere and even more over the poles. These observations are in general agreement with model predictions made with the Whole Atmosphere Community Climate Model (WACCM). A detailed 3-D chemical transport model is needed to account for the global isotopic distributions of N2O and to infer sources and sinks. [ABSTRACT FROM AUTHOR]

MIPAS thermal limb emission measurements were used to derive vertically resolved profiles of carbon tetrachloride (CCl4). Level-1b data versions MIPAS/5.02 to MIPAS/5.06 were converted into volume mixing ratio profiles using the level-2 processor developed at Karlsruhe Institute of Technology (KIT) Institute of Meteorology and Climate Research (IMK) and Consejo Superior de Investigaciones Científicas (CSIC), Instituto de Astrofísica de Andalucía (IAA). Consideration of peroxyacetyl nitrate (PAN) as an interfering species, which is jointly retrieved, and CO2 line mixing is crucial for reliable retrievals. Parts of the CO2 Q-branch region that overlap with the CCl4 signature were omitted, since large residuals were still found even though line mixing was considered in the forward model. However, the omitted spectral region could be narrowed noticeably when line mixing was accounted for. A new CCl4 spectroscopic data set leads to slightly smaller CCl4 volume mixing ratios. In general, latitude-altitude cross sections show the expected CCl4 features with highest values of around 90 pptv at altitudes at and below the tropical tropopause and values decreasing with altitude and latitude due to stratospheric decomposition. Other patterns, such as subsidence in the polar vortex during winter and early spring, are also visible in the distributions. The decline in CCl4 abundance during the MIPAS Envisat measurement period (July 2002 to April 2012) is clearly reflected in the altitude-latitude cross section of trends estimated from the entire retrieved data set. [ABSTRACT FROM AUTHOR]

It is known from ground-based measurements made during the 1982-83 and 1997-98 El Niño events that atmospheric HCN tends to be higher than usual during such years. The Microwave Limb Sounder (MLS) on Aura has been measuring HCN mixing ratios since launch in 2004; the measurements are ongoing at the time of writing. The winter of 2015-16 has seen the largest El Niño event since 1997-98. We present MLS measurements of HCN in the lower stratosphere for the Aura mission to date, comparing the 2015-16 El Niño period to the rest of the mission. HCN in 2015-16 is higher than at any other time during the mission, but ground based measurements suggest that it may have been even more elevated in 1997-98. As the MLS HCN data are essentially un-validated, we show them alongside data from the MIPAS and ACE-FTS instruments; the three instruments agree reasonably well in the tropical lower stratosphere. Global HCN emissions calculated from the GFED (V4.1) database are very much greater during large El Niño events and are greater in 1997-98 than in 2015-16, thereby showing good qualitative agreement with the measurements. Correlation between ENSO indices, measured HCN and GFED HCN emissions is less clear away from the 2015-16 event. In particular, the 2009-10 winter had fairly strong El Niño conditions and fairly large GFED HCN emissions, but very little effect is observed in the MLS HCN. [ABSTRACT FROM AUTHOR]

MIPAS thermal limb emission measurements were used to derive vertically resolved profiles of carbon tetrachloride (CCl4). Level-1b data versions MIPAS/5.02 to MIPAS/5.06 were converted into profiles using the level-2 processor developed at Karlsruhe Institute of Technology (KIT) Institute of Meteorology and Climate Research (IMK) and Consejo Superior de Investigaciones Científicas (CSIC), Instituto de Astrofísica de Andalucía (IAA). Consideration of peroxyacetyl nitrate (PAN) as interfering species, which is jointly retrieved and CO2 line mixing, was found to be crucial for reliable retrievals. Parts of the CO2 Q-branch region that overlap with the CCl4 signature were omitted, since large residuals were still found even though line mixing was considered in the forward model. However, the omitted spectral region could be narrowed considerably when line mixing was a44 volume mixing ratios. In general, latitude-altitude cross-section show the expected CCl4 features with highest values of around 90 pptv at altitudes at and below the tropical tropopause and values decreasing with altitude and latitude due to stratospheric decomposition. Other patterns, such as subsidence in the polar vortex during winter and early spring, are also visible in the distributions. The decline in CCl4 abundance during the MIPAS Envisat measurement period (July 2002 to April 2012) is clearly reflected in the retrieved distributions. [ABSTRACT FROM AUTHOR]

The ACE-FTS (Atmospheric Chemistry Experiment - Fourier Transform Spectrometer) instrument on the Canadian SCISAT satellite, which has been in operation for over 12 years, has the capability of deriving stratospheric profiles of many of the NOy (N + NO + NO2+ NO3 + 2 x N2O5+ HNO3 + HNO4 + ClONO2 + BrONO2) species. Version 2.2 of ACE-FTS NO, NO2, HNO3, N2O5, and ClONO2 has previously been validated, and this study compares the most recent version (v3.5) of these five ACE-FTS products to spatially and temporally coincident measurements from other satellite instruments - GOMOS, HALOE, MAESTRO, MIPAS, MLS, OSIRIS, POAM III, SAGE III, SCIA-MACHY, SMILES, and SMR. For each ACE-FTS measurement, a photochemical box model was used to simulate the diurnal variations of the NOy species and the ACE-FTS measurements were scaled to the local times of the coincident measurements. The comparisons for all five species show good agreement with correlative satellite measurements. For NO in the altitude range of 25-50 km, ACE-FTS typically agrees with correlative data to within -10%. Instrument-averaged mean relative differences are approximately -10 % at 30-40 km for NO2, within ± 7% at 8-30km for HNO3, better than -7 % at 21-34 km for local morning N2O5, and better than -8 % at 21-34km for ClONO2. Where possible, the variations in the mean differences due to changes in the comparison local time and latitude are also discussed. [ABSTRACT FROM AUTHOR]

Peroxyacetyl nitrate (PAN) is an important chemical species in the troposphere as it aids the long-range transport of NOx and subsequent formation of O3 in relatively clean remote regions. Over the past few decades observations from aircraft campaigns and surface sites have been used to better understand the regional distribution of PAN. However, recent measurements made by satellites allow for a global assessment of PAN in the upper troposphere-lower stratosphere (UTLS). In this study, we investigate global PAN distributions from two independent retrieval methodologies, based on measurements from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) instrument, on board Envisat from the Institute of Meteorology and Climate Research (IMK), Karlsruhe Institute of Technology, and the Department of Physics and Astronomy, University of Leicester (UoL). Retrieving PAN from MIPAS is challenging due to the weak signal in the measurements and contamination from other species. Therefore, we compare the two MIPAS datasets with observations from the Atmospheric Chemistry Experiment Fourier transform spectrometer (ACE-FTS), in situ aircraft data and the 3-D chemical transport model TOMCAT. MIPAS shows peak UTLS PAN concentrations over the biomass burning regions (e.g. ranging from 150 to > 200 pptv at 150 hPa) and during the summertime Asian monsoon as enhanced convection aids the vertical transport of PAN from the lower atmosphere. At 150 hPa, we find significant differences between the two MIPAS datasets in the tropics, where IMK PAN concentrations are larger by 50-100 pptv. Comparisons between MIPAS and ACE-FTS show better agreement with the UoL MIPAS PAN concentrations at 200 hPa, but with mixed results above this altitude. TOMCAT generally captures the magnitude and structure of climatological aircraft PAN profiles within the observational variability allowing it to be used to investigate the MIPAS PAN differences. TOMCAT-MIPAS comparisons show that the model is both positively (UoL) and negatively (IMK) biased against the satellite products. These results indicate that satellite PAN observations are able to detect realistic spatial variations in PAN in the UTLS, but further work is needed to resolve differences in existing retrievals to allow quantitative use of the products. [ABSTRACT FROM AUTHOR]

The vast majority of emissions of fluorine-containing molecules are anthropogenic in nature, e.g. chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbons (HFCs). Many of these fluorine-containing species deplete stratospheric ozone and are regulated by the Montreal Protocol. Once in the atmosphere they slowly degrade, ultimately leading to the formation of hydrogen fluoride (HF), the dominant reservoir of stratospheric fluorine due to its extreme stability. Monitoring the growth of stratospheric HF is therefore an important marker for the success of the Montreal Protocol. We report the comparison of global distributions and trends of HF measured in the Earth's atmosphere by the satellite remote-sensing instruments ACE-FTS (Atmospheric Chemistry Experiment Fourier transform spectrometer), which has been recording atmospheric spectra since 2004, and HALOE (HALogen Occultation Experiment), which recorded atmospheric spectra between 1991 and 2005, with the output of SLIMCAT, a state-of-the-art three-dimensional chemical transport model. In general the agreement between observation and model is good, although the ACE-FTS measurements are biased high by ∼ 10% relative to HALOE. The observed global HF trends reveal a substantial slowing down in the rate of increase of HF since the 1990s: 4.97 - 0.12% year-1 (1991-1997; HALOE), 1.12 - 0.08% year-1 (1998-2005; HALOE), and 0.52 - 0.03% year-1 (2004-2012; ACE-FTS). In comparison, SLIMCAT calculates trends of 4.01, 1.10, and 0.48% year-1, respectively, for the same periods; the agreement is very good for all but the earlier of the two HALOE periods. Furthermore, the observations reveal variations in the HF trends with latitude and altitude; for example, between 2004 and 2012 HF actually decreased in the Southern Hemisphere below ∼ 35 km. An additional SLIMCAT simulation with repeating meteorology for the year 2000 produces much cleaner trends in HF with minimal variations with latitude and altitude. Therefore, the variations with latitude and altitude in the observed HF trends are due to variability in stratospheric dynamics on the timescale of a few years. Overall, the agreement between observation and model points towards the ongoing success of the Montreal Protocol and the usefulness of HF as a metric for stratospheric fluorine. [ABSTRACT FROM AUTHOR]

This paper presents an analysis of observations of methane and its two major isotopologues, CH3D and 13CH4, from the Atmospheric Chemistry Experiment (ACE) satellite between 2004 and 2013. Additionally, atmospheric methane chemistry is modeled using the Whole Atmospheric Community Climate Model (WACCM). ACE retrievals of methane extend from 6 km for all isotopologues to 75 km for 12CH4, 35 km for CH3D, and 50 km for 13CH4. While total methane concentrations retrieved from ACE agree well with the model, values of δD-CH4 and δ13C-CH4 show a bias toward higher δ compared to the model and balloon-based measurements. Errors in spectroscopic constants used during the retrieval process are the primary source of this disagreement. Calibrating δD and δ13C from ACE using WACCM in the troposphere gives improved agreement in δD in the stratosphere with the balloon measurements, but values of δ13C still disagree. A model analysis of methane's atmospheric sinks is also performed. [ABSTRACT FROM AUTHOR]

This paper presents an analysis of observations of methane and its two major isotopologues, CH3D and 13CH4, from the Atmospheric Chemistry Experiment (ACE) satellite between 2004 and 2013. Additionally, atmospheric methane chemistry is modeled using the Whole Atmospheric Community Climate Model (WACCM). ACE retrievals of methane extend from 6 km for all isotopologues to 75 km for 12CH4, 35km for CH3D, and 50km for 13CH4. While total methane concentrations retrieved from ACE agree well with the model, values of δD-CH4 and δ 13C-CH4 show δ bias toward higher δ compared to the model and balloon-based measurements. Errors in spectroscopic constants used during the retrieval process are the primary source of this disagreement. Calibrating 5D and 513C from ACE using WACCM in the troposphere gives improved agreement in 5D in the stratosphere with the balloon measurements, but values of δ13C still disagree. A model analysis of methane's atmospheric sinks is also performed. [ABSTRACT FROM AUTHOR]

The impact of volcanic eruptions on water vapour in the high-latitude upper troposphere is studied using deseasonalized time series based on observations by the Atmospheric Chemistry Experiment (ACE) water vapour sensors, namely MAESTRO (Measurements of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation) and the Fourier Transform Spectrometer (ACE-FTS). The two eruptions with the greatest impact on the high-latitude upper troposphere during the time frame of this satellite-based remote sensing mission are chosen. The Puyehue-Cordón Caulle volcanic eruption in June 2011 was the most explosive in the past 24 years and is shown to be able to account for the observed (50 ± 12)% increase in water vapour in the southern high-latitude upper troposphere in July 2011 after a minor adjustment for the simultaneous influence of the Antarctic oscillation. Eyjafjallajökull erupted in the spring of 2010, increasing water vapour in the upper troposphere at northern high latitudes significantly for a period of ~ 1 month. These findings imply that extratropical volcanic eruptions in windy environments can lead to significant perturbations to high-latitude upper tropospheric humidity mostly due to entrainment of lower tropospheric moisture by wind-blown plumes. The Puyehue-Cordón Caulle eruption must be taken into account to properly determine the magnitude of the trend in southern high-latitude upper tropospheric water vapour over the last decade. [ABSTRACT FROM AUTHOR]

The dipole moment is one of the most important physical properties of a molecule. We present a combination rule for the dipole moments of related diatomic molecules. For molecules AB, AX, BY, and XY from two different element groups in the periodic table, if their elements make a small parallelogram, reliable predictions can be obtained. Our approach is particularly useful for systems with heavy atoms. For a large set of molecules tested, the average difference of the prediction from experimental data is less than 0.2 debye (D). The dipole moments for heavy molecules such as GaCl, InBr, SrCl, and SrS, for which no experimental data are available at present, are predicted to be 3.17, 3.76, 3.85 and 11.54 D, respectively. [ABSTRACT FROM AUTHOR]

The report of an IUPAC Task Group, formed in 2011 on 'Intensities and line shapes in high-resolution spectra of water isotopologues from experiment and theory' (Project No. 2011-022-2-100), on line profiles of isolated high-resolution rotational-vibrational transitions perturbed by neutral gas-phase molecules is presented. The well-documented inadequacies of the Voigt profile (VP), used almost universally by databases and radiative-transfer codes, to represent pressure effects and Doppler broadening in isolated vibrational-rotational and pure rotational transitions of the water molecule have resulted in the development of a variety of alternative line-profile models. These models capture more of the physics of the influence of pressure on line shapes but, in general, at the price of greater complexity. The Task Group recommends that the partially Correlated quadratic-Speed-Dependent Hard-Collision profile (pCqSD-HCP) should be adopted as the appropriate model for high-resolution spectroscopy. For simplicity this should be called the Hartmann-Tran profile (HTP). The HTP is sophisticated enough to capture the various collisional contributions to the isolated line shape, can be computed in a straightforward and rapid manner, and reduces to simpler profiles, including the Voigt profile, under certain simplifying assumptions. [ABSTRACT FROM AUTHOR]

Accurate rotation–vibration line lists for two molecules, NaCl and KCl, in their ground electronic states are presented. These line lists are suitable for temperatures relevant to exoplanetary atmospheres and cool stars (up to 3000 K). Isotopologues 23Na35Cl, 23Na37Cl, 39K35Cl, 39K37Cl, 41K35Cl and 41K37Cl are considered. Laboratory data were used to refine ab initio potential energy curves in order to compute accurate ro-vibrational energy levels. Einstein Acoefficients are generated using newly determined ab initio dipole moment curves calculated using the CCSD(T) method. New Dunham Yij constants for KCl are generated by a re-analysis of a published Fourier transform infrared emission spectra. Partition functions plus full line lists of ro-vibration transitions are made available in an electronic form as supplementary data to this paper and at www.exomol.com. [ABSTRACT FROM AUTHOR]

The report and results of an IUPAC Task Group (TG) formed in 2004 on 'A Database of Water Transitions from Experiment and Theory' (Project No. 2004-035-1-100) are presented. Energy levels and recommended labels involving exact and approximate quantum numbers for the main isotopologues of water in the gas phase, H216O, H218O, H217O, HD16O, HD18O, HD17O, D216O, D218O, and D217O, are determined from measured transition frequencies. The transition frequencies and energy levels are validated using first-principles nuclear motion computations and the MARVEL (measured active rotational-vibrational energy levels) approach. The extensive data including lines and levels are required for analysis and synthesis of spectra, thermochemical applications, the construction of theoretical models, and the removal of spectral contamination by ubiquitous water lines. These datasets can also be used to assess where measurements are lacking for each isotopologue and to provide accurate frequencies for many yet-to-be measured transitions. The lack of high-quality frequency calibration standards in the near infrared is identified as an issue that has hindered the determination of high-accuracy energy levels at higher frequencies. The generation of spectra using the MARVEL energy levels combined with transition intensities computed using high accuracy ab initio dipole moment surfaces are discussed. A recommendation of the TG is for further work to identify a single, suitable model to represent pressure- (and temperature-) dependent line profiles more accurately than Voigt profiles. [ABSTRACT FROM AUTHOR]