The oxygen A-band (760 nm) is used in a number of remote sensing applications due to the precisely known, uniform distribution of molecular oxygen throughout the atmosphere and the spectral isolation of the band. The A-band is used to determine the pathlength of solar radiation for OCO-2, a current NASA mission which seeks to measure the global sources and sinks of carbon dioxide at unprecedented spatial and temporal resolution. The goal of measuring atmospheric carbon dioxide concentrations with a precision of 0.25% requires a precise knowledge of line shape parameters. Currently, the most significant uncertainties in A-band spectroscopy result from line mixing and collision induced absorption, which become more prominent at elevated pressures. Photoacoustic spectroscopy is ideal to observe these phenomena due to the large dynamic range and zero-background advantages of the technique. Photoacoustic spectra of the oxygen A-band over a range of pressures will be presented in addition to line shape parameters extracted from multispectrum fits of the data.

Composition measurements from remote sensing platforms require knowledge of air mass to better than the desired precision of the composition. Oxygen spectra allow determination of air mass since the mixing ratio of oxygen is fixed. The OCO-2 mission is currently retrieving carbon dioxide concentration using the oxygen A-band for air mass normalization. The 0.25% accuracy desired for the carbon dioxide concentration has pushed the state-of-the-art for oxygen spectroscopy. To produce atmospheric pressure A-band cross-sections with this accuracy requires a sophisticated line-shape model (Galatry or Speed-Dependent) with line mixing (LM) and collision induced absorption (CIA). Models of each of these phenomena exist, but an integrated self-consistent model must be developed to ensure accuracy. This presentation will describe the ongoing effort to parameterize these phenomena on a representative data set created from complementary experimental techniques. The techniques include Fourier transform spectroscopy (FTS), photo-acoustic spectroscopy (PAS) and cavity ring-down spectroscopy (CRDS). CRDS data allow long-pathlength measurements with absolute intensities, providing lineshape information as well as LM and CIA, however the subtleties of the lineshape are diminished in the saturated line-centers. Conversely, the short paths and large dynamic range of the PAS data allow the full lineshape to be discerned, but with an arbitrary intensity axis. Finally, the FTS data provides intermediate paths and consistency across a broad pressure range. These spectra are all modeled with the Labfit software using first the spectral line database HITRAN, and then model values are adjusted and fitted for better agreement with the data.

We report precise line areas for individual rotationally resolved transitions within the a¹∆_g← X³Σ⁻_g electronic band of molecular oxygen recorded as a function of pressure for both neat samples of O₂ as well as samples of O₂ dilute with a variety of collisional partners. Using optical frequency comb referenced frequency-stabilized cavity ring-down spectroscopy (FS-CRDS) near 1.27 μm we measure line areas with a quality-of-fit QF ≤ 50,000 using a partially correlated quadratic-speed-dependent Nelkin-Ghatak profile. This spectrometer has achieved this high QF by both suppressing coupled cavity effects and by preserving a high-fidelity frequency axis with absolute frequency accuracy approaching 1 part in 10⁹. With this instrument we are also currently exploring collision-induced absorption (CIA) and perturbative line mixing effects in O₂ over the entire 7800-7940 cm⁻¹spectral range.

The HDO molecule is important from the atmospheric point of view as it can be used to study the water cycle in the earth atmosphere.Herbin et al., Atmos. Chem. Phys.  9 (2009) 9433; and Schneider and Hase, Atmos. Chem.\ Phys. 11 (2011) 11207.t is also interesting from the spectroscopic point of view as it displays an anomalous centrifugal distortion similar to that of the normal species H₂O. A model developed to treat the anomalous distortion in HDO should account for the fact that it lacks a two-fold axis of symmetry. A new treatment aimed at the calculation of the rovibrational energy of the HDO molecule and allowing for anomalous centrifugal distortion effects has been developed. It is based on an effective Hamiltonian in which the large amplitude bending ν₂ mode and the overall rotation of the molecule are treated simultaneously.Coudert, Wagner, Birk, Baranov, Lafferty, and Flaud, J. Molec. Spectrosc.  251 (2008) 339.ue to the lack of a two-fold axis of symmetry, this effective Hamiltonian contains terms arising from the non-diagonal component of the inertia tensor and from the Coriolis-coupling between the large amplitude bending ν₂ mode and the overall rotation of the molecule. This new treatment has been used to perform a line position analysis of a large body of infrared,Johns, J. Opt. Soc. Am. B 2 (1985) 1340; Toth, J.\ Molec. Spectrosc. 162 (1993) 20; Paso and Horneman, J. Opt. Soc. Am. B 12 (1995) 1813; and Toth, J. Molec. Spectrosc. 195 (1999) 73.icrowave,Messer, De Lucia, and Helminger, J. Molec. Spectrosc. 105 (1984) 139; and Baskakov et al., Opt. Spectrosc. 63 (1987) 1016.nd hot water vaporParekunnel et al., J. Molec.\ Spectrosc. 210 (2001) 28; and Janca et al., J.\ Molec. Specrosc. 219 (2003) 132.ata involving the ground and (010) states up to J=22. For these 4413 data, a unitless standard deviation of 1.1 was achieved. A line intensity analysis was also carried out and allowed us to reproduce the strength of 1316 transitions^c with a unitless standard deviation of 1.1. In the talk, the new theoretical approach will be presented. The results of both analyses will be discussed and compared with those of a previous investigation.Tennyson et al., J. Quant.\ Spectrosc. Radiat. Transfer 111 (2010) 2160.he new spectroscopic data base built will be compared with HITRAN 2012.Rothman et al., J. Quant. Spectrosc.\ Radiat. Transfer 130 (2013) 4.html:<hr /><h3>Footnotes: Herbin et al., Atmos. Chem. Phys.  9 (2009) 9433; and Schneider and Hase, Atmos. Chem.\ Phys. 11 (2011) 11207.I Coudert, Wagner, Birk, Baranov, Lafferty, and Flaud, J. Molec. Spectrosc.  251 (2008) 339.D Johns, J. Opt. Soc. Am. B 2 (1985) 1340; Toth, J.\ Molec. Spectrosc. 162 (1993) 20; Paso and Horneman, J. Opt. Soc. Am. B 12 (1995) 1813; and Toth, J. Molec. Spectrosc. 195 (1999) 73.m Messer, De Lucia, and Helminger, J. Molec. Spectrosc. 105 (1984) 139; and Baskakov et al., Opt. Spectrosc. 63 (1987) 1016.a Parekunnel et al., J. Molec.\ Spectrosc. 210 (2001) 28; and Janca et al., J.\ Molec. Specrosc. 219 (2003) 132.d Tennyson et al., J. Quant.\ Spectrosc. Radiat. Transfer 111 (2010) 2160.T Rothman et al., J. Quant. Spectrosc.\ Radiat. Transfer 130 (2013) 4.

Climate change is one of the greatest challenges presently facing mankind, and methane is one of the most powerful anthropogenic greenhouse gases. For a better understanding of future climate trends, a satellite dedicated to the measurements of atmospheric methane is under joint development by the French and German space research centers (CNES and DLR). The so-called MERLIN mission (Methane Remote Sensing Lidar Mission, 2019) aims at providing global information on atmospheric methane concentration with a relative uncertainty less than 2% and with a spatial resolution of 50 kmC. Kiemle, M. Quatrevalet, G. Ehret et al., Atmos. Meas. Tech. 4 (2011) Such spectroscopic monitoring of gases in the atmosphere of the Earth, requires a precise description of absorption lines shapes that goes beyond the usual Voigt profile (VP). In the case of methane, the differences between the measured profiles and those given by the VP can be very important H. Tran, J.-M. Hartmann, G. Toon et al., Journal of Quant. Spectrosc. Radia. Trans. 111 (2010) making the VP completely incompatible with the reliable detection of sources and sinks from space. In this work, we present the first results on the modeling of methane lines broadened by air in the 1.64 μm region and the associated spectroscopic parameters, taking into account various collisional effects between molecules that are neglected by the VP: collisional interference between the lines (line-mixing), collision-induced velocity changes (Dicke narrowing effect) and speed dependence of the collisional broadening and shifting. These results were obtained by simultaneously fitting the model parameters to high sensitivity and high-resolution cavity ring-down spectroscopy (CRDS) spectra recorded at the National Institute of Standards and Technology (NIST) over a wide pressure range (5 to 100 kPa). These spectroscopic data and the associated model to calculate the spectrum absorption coefficient will be then used to analyze ground-based atmospheric spectra at the TCCON facility in Park Falls, Wisconsin.

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Footnotes:

C. Kiemle, M. Quatrevalet, G. Ehret et al., Atmos. Meas. Tech. 4 (2011). H. Tran, J.-M. Hartmann, G. Toon et al., Journal of Quant. Spectrosc. Radia. Trans. 111 (2010),

Line parameter errors can contribute significantly to the total errors in retrievals of terrestrial atmospheric ozone concentration profiles using the strong 9.6-μm band, particularly for nadir-viewing experimentsJ. Worden et al., J. Geophys. Res. 109 (2004) 9308-9319. Detailed knowledge of the interfering ozone signal is also needed for retrievals of other atmospheric speciesR. Beer et al., Geophys. Res. Lett. 35 (2008) L09801.n this spectral region. We have determined Lorentz air-broadening and pressure-induced shift coefficients along with their temperature dependences for a number of transitions in the ν₃ fundamental band of ¹⁶O₃. These results were obtained by applying the multispectrum nonlinear least-squares fitting techniqueD. Chris Benner et al., JQSRT 53 (1995) 705-721.o a set of 31 high-resolution infrared absorption spectra of O₃ recorded at temperatures between 160 and 300 K with several different room-temperature and coolable sample cells at the McMath-Pierce Fourier transform spectrometer at the National Solar Observatory on Kitt Peak. We compare our results with other available measurements and with the ozone line parameters in the HITRAN databaseL. S. Rothman et al., JQSRT 130 (2013) 4-50.

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Footnotes:

J. Worden et al., J. Geophys. Res. 109 (2004) 9308-9319.. R. Beer et al., Geophys. Res. Lett. 35 (2008) L09801.i D. Chris Benner et al., JQSRT 53 (1995) 705-721.t L. S. Rothman et al., JQSRT 130 (2013) 4-50..

In 1989 the Lineberger group observed S₀ vinylidene in the negative ion photoelectron spectrum. Excess widths were interpreted by some as indicating a sub-picosecond lifetime for vinylidene. 1998 Coulomb explosion experiments showed that vinylidene character survives for at least 3.5 μs. Chirped Pulse mm-Wave spectra showed that 193 nm photolysis of Vinyl Cyanide produces many vibrational levels of HCN and HNC but no trace of vinylidene or local-bender excited acetylene. David Perry’s and Michel Herman’s effective Hamiltonian model for local-bender acetylene showed that IVR is complete at J approximately 100. Observation of long-lived vinylidene requires formation at low-J. Photodetachment of an electron from the Vinylidene negative ion deposits negligible angular momentum in the C₂H₂ moiety. The high-resolution negative-ion Photoelectron Velocity Map Imaging spectrometer at ANU reveals vinylidene with strongly vibration-dependent β asymmetry parameters. Infrared Multi-Photon Dissociation of Vinyl Chloride in the Wayne State Velocity Map Imaging spectrometer reveals rotationally and vibrationally cold HCl, presumably the 3-center photofragmentation co-product of rotationally cold vinylidene. The mechanism of vinylidene-acetylene isomerization is emerging…

A new set of line parameters (positions, intensities and line widths) for nitric acid has been generated in the 7.6 μm region using the results of recent high quality experimental laboratory studies and of theoretical calculations. The validation of this new database was performed thanks to limb emission radiances measured in 2002-2012 by the "Michelson Interferometer for Passive Atmospheric Sounding" (MIPAS) instrument on board the ENVISAT satellite. This study will help to improve HNO₃ satellite retrievals by allowing measurements to be performed using simultaneously 11 μm and 7.6 μm microwindows. Hopefully this will be the case for the forthcoming Infrared Atmospheric Sounding Interferometer New Generation (IASI-NG) instrument developed by CNES. IASI-NG will be the key payload element of the future METOP Second Generation (METOP-SG) series of EUMETSAT meteorological polar-orbit satellites.

In a recent study of unpolluted air samples from Tasmania and of deep firn snow in Greenland four previously overlooked ozone-depleting substances have been identified.J.C.Laube, et al., Nature Geoscience 7, 266 (2014).hese compounds started to emerge in the atmosphere in the 1960s, and two: CF₃CCl₃ (CFC-113a) and CF₃CH₂Cl (HCHF-133a) continue to accumulate in the atmosphere. Three of the four compounds have non-zero dipole moments and are amenable to study by rotational spectroscopy, establishing the basis for analytic applications. Relatively limited studies have been reported for CF₃CH₂ClT.Ogata, et al., J. Mol. Struct. 144, 1 (1986).nd CF₃CCl₃,R.Holm, et al., Z. Naturforsch. 23a, 1040 (1968).^,J.H.Carpenter et al.,J. Mol. Spectrosc. 154, 207 (1992); P.J.Seo et al., J. Mol. Spectrosc. 169, 58 (1995).hile CF_2ClCCl_3 J.H.Carpenter et al.,J. Mol. Spectrosc. 154, 207 (1992); P.J.Seo et al., J. Mol. Spectrosc. 169, 58 (1995).w

Amine-carboxylic acid interactions are important in many biological systems and have recently received attention for their role in the formation of atmospheric aerosols. Here, we study the molecular and electronic structure of the formic acid – trimethylamine complex, using it as a model for amine-carboxylic acid interactions. The microwave spectrum of the complex has been observed using chirped pulse and conventional cavity-type Fourier transform microwave spectroscopy. The degree of proton transfer has been assessed using the ¹⁴N nuclear quadrupole hyperfine structure. Experimental results will be compared to DFT calculations.

Aerosols are important players in the Earth’s atmosphere, affecting climate, cloud formation, and human health. In this work, we report the discovery of a previously unknown molecule, formic sulfuric anhydride (FSA), that may influence the formation and composition of atmospheric aerosol particles. Five isotopologues of FSA have been observed by microwave spectroscopy and further characterized using DFT calculations. The system has dipole moment components along all three inertial axes, and indeed a, b, and c-type transitions have been observed. A π₂ + π₂ + σ₂ cycloaddition reaction between SO₃ and HCOOH is proposed as a possible mechanism for the formation of FSA and calculations indicate that the transformation is effectively barrierless. Facile formation of the anhydride followed by hydrolysis in small water-containing clusters or liquid droplets may provide a mechanism of incorporating volatile organics into atmospheric aerosol. We suggest that FSA and its derivatives be considered in future atmospheric and climate models.

Last year we reported the analysis of the rotational spectrum of s-trans conformer of methacrolein CH₂=C(CH₃)CHO in the ground vibrational stateZakharenko O. et al., 69th ISMS, 2014, TI01 In this talk we report the study of its low lying excited vibrational states. The study is based on room-temperature absorption spectra of methacrolein recorded in the frequency range 150 – 465 GHz using the spectrometer in Lille. The new results include assignment of the first excited torsional state (131 cm⁻¹), and the joint analysis of the v_t = 0 and v_t = 1 states, that allowed us to improve the model in the frame of Rho-Axis-Method (RAM) Hamiltonian and to remove some strong correlations between parameters. Also we assigned the first excited vibrational state of the skeletal torsion mode (170 cm⁻¹). The inverse sequence of A and E tunneling substates as well as anomalous A-E splittings observed for the rotational lines of v_sk = 1 state clearly indicate a coupling between methyl torsion and skeletal torsion. However we were able to fit within experimental accuracy the rotational lines of v_sk = 1 state using the RAM Hamiltonian. Because of the inversion of the A and E tunneling substates the rotational lines of the v_sk = 1 states were assumed to belong to a virtual first excited torsional state. Finally, we assigned several low-K_a rotational transitions of the excited vibrational states above 200 cm⁻¹ but their analysis is complicated by different rotation-vibration interactions. In particular there is an evidence of the Fermi-type resonance between the second excited torsional state and the first excited state of the in-plane skeletal bending mode (265 cm⁻¹).
Support from the French Laboratoire d’Excellence CaPPA (Chemical and Physical Properties of the Atmosphere) through contract ANR-10-LABX-0005 of the Programme d’Investissements d’Avenir is acknowledged.

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Footnotes:

Zakharenko O. et al., 69th ISMS, 2014, TI01.

Methyl vinyl ketone, MVK, along with previously studied by our team methacrolein, is a major oxidation product of isoprene, which is one of the primary contributors to annual global VOC emissions. In this talk we present the analysis of the rotational spectrum of MVK recorded at room temperature in the 50 - 650 GHz region using the Lille spectrometer. The spectroscopic characterization of MVK ground state will be useful in the detailed analysis of high resolution infrared spectra. Our study is supported by high level quantum chemical calculations to model the structure of the two stable s-trans and s-cis conformers and to obtain the harmonic force field parameters, internal rotation barrier heights, and vibrational frequencies. In the Doppler-limited spectra the splittings due to the internal rotation of methyl group are resolved, therefore for analysis of this molecule we used the Rho-Axis-Method Hamiltonian and RAM36 code to fit the rotational transitions. At the present time the ground state of two conformers is analyzed. Also we intend to study some low lying excited states. The analysis is in progress and the latest results will be presented.
Support from the French Laboratoire d’Excellence CaPPA (Chemical and Physical Properties of the Atmosphere) through contract ANR-10-LABX-0005 of the Programme d’Investissements d’Avenir is acknowledged.