Carbonyl oxides (R₁R₂COO), also known as Criegee intermediates (CIs), react quickly with many trace atmospheric gases, including inorganic gases such as HCl, which are present in polluted urban atmospheres. A theoretical investigation of the reaction between the simplest CI, CH₂OO, with HCl suggests the formation of chloromethyl hydroperoxide (CMHP) through an insertion mechanism. To gain some insight, we have interrogated the reaction system containing CH₂OO and HCl through pure rotational spectroscopy. In our experiment, CH₂OO molecules have been generated in the discharged plasma of a CH₂I₂/O₂ mixture, which containg a small amount of HCl enough to react with CH₂OO. The resulting products (including CH₂OO) were characterized by Fourier-transform microwave (FTMW) spectroscopy. Rotational transitions in the 6-40 GHz frequency range were observed by FTMW spectroscopy together with FTMW-mmW and MW-MW double-resonance techniques. The observed species was identified with the help of quantum chemical calculations as the most stable conformer of CMHP. The non observation of other different reaction products together with the absence of spectral features of the complex between HCl and CH₂OO enable us to understand the pathway of the HCl+CH₂OO reaction.

Carbonyl oxides (R₁R₂COO), often called Criegee intermediates (CIs), have been assumed as intermediates generated by the ozonolysis reaction of alkenes, and are thought to play important roles in atmospheric chemistry. After the first laboratory observation of the simplest CI, CH₂OO, their experimental characterization has been drastically progressing. Especially alkyl-substituted CIs have attracted much attention. Here we report rotational spectra of alkyl-substituted CIs with three carbon atoms in the substituent groups, named C₃ alkyl-substituted CIs. This group includes methyl-ethyl-ketone oxide or 2-butanone oxide (C₂H₅CCH₃OO) and its structural isomers n-butyraldehyde oxide (C₃H₇CHOO) and isobutyraldehyde oxide ((CH₃)₂CHCHOO). These molecules have been produced in the discharge plasma of diiodo-alkyl-derivative/O₂ gas mixtures, and characterized by Fourier-transform microwave spectroscopy. For the first of them, C₂H₅CCH₃OO, four different conformers were observed coexisting in the supersonic expansion. Spectra of the four species show small splittings due to the threefold methyl internal rotation which made possible to determine their respective barrier heights of the hindered methyl rotation. Preliminary results of the ongoing investigation of C₃H₇CHOO and (CH₃)₂CHCHOO molecules are also presented.

Sulfur trioxide reacts with propiolic acid and acrylic acid to form propiolic sulfuric anhydride (HC ≡ C-COOSO₂OH) and acrylic sulfuric anhydride (H₂C=CH-COOSO₂OH), respectively. Both species have been observed by chirped-pulse and conventional cavity microwave spectroscopy. In the case of acrylic acid, two conformers derived from the cis and trans form of the acid have been observed. The reaction mechanism and energetics are investigated by density functional theory and CCSD calculations. These results add to a growing body of evidence that establishes carboxylic sulfuric anhydrides, RCOOSO₂OH, as a class of molecules formed readily from SO₃ + RCOOH in the gas phase and which, therefore, may be of significance in the nucleation and growth of atmospheric aerosol particles.

Sulfur trioxide and acetic acid are shown to react under supersonic jet conditions to form acetic sulfuric anhydride, CH₃COOSO₂OH. Rotational spectra of the parent, ³⁴S, methyl ¹³C, and fully deuterated isotopologues have been observed by chirped-pulse and conventional cavity microwave spectroscopy. A and E internal rotation states have been observed for each isotopologue studied and the methyl group internal rotation barriers have been determined (241.043(65) cm⁻¹for the parent species). The reaction is analogous to that of our previous report on the reaction of sulfur trioxide and formic acid. DFT and CCSD calculations are also presented which indicate that the reaction proceeds via a π₂ + π₂ + σ₂ cycloaddition reaction. These results support our previous conjecture that the reaction of SO₃ with carboxylic acids is both facile and general. Possible implications for atmospheric aerosol formation are discussed.

A Bruker IFS 120HR Fourier transform spectrometer (FTS) at the Pacific Northwest National Laboratory (PNNL) in Richland, Washington was used to record a series of spectra in the regions of the ν₁ and ν₃ bands of H₂O. The samples included low pressures of pure H₂O as well as H₂O broadened by air at different pressures, temperatures and volume mixing ratios. We fit simultaneously 16 high-resolution (0.008 cm⁻¹), high S/N ratio absorption spectra recorded at 268, 296 and 353 K (L=19.95 cm), employing a multispectrum fitting techniqueD. C. Benner, C. P. Rinsland, V. Malathy Devi, M. A. H. Smith, D. Atkins, JQSRT 53 (1995) 705-721.o retrieve accurate line positions, relative intensities, Lorentz air-broadened half-width and pressure-shift coefficients and their temperature dependences for more than 220 H₂O transitions. Self-broadened half-width and self-shift coefficients were measured for over 100 transitions. For select sets of transition pairs for the H₂O-air system we determined collisional line mixing coefficients via the off-diagonal relaxation matrix element formalismA. Levy, N. Lacome, C. Chackerian, Collisional line mixing, in Spectroscopy of the Earth′s Atmosphere and Interstellar Medium, Academic Press, Inc., Boston (1992) 261-337. and we also measured speed dependence parameters for 85 transitions. Modified Complex Robert Bonamy (MCRB) calculations of the half-widths, line shifts, and temperature dependences were made for self-, N₂-, O₂-, and air-broadening. The measurements and calculations are compared with each other and with similar parameters reported in the literature.

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Footnotes:

D. C. Benner, C. P. Rinsland, V. Malathy Devi, M. A. H. Smith, D. Atkins, JQSRT 53 (1995) 705-721.t A. Levy, N. Lacome, C. Chackerian, Collisional line mixing, in Spectroscopy of the Earth′s Atmosphere and Interstellar Medium, Academic Press, Inc., Boston (1992) 261-337.,

We present results of a recent analysis of laboratory spectra to determine line positions, intensities, air-broadened half-widths and pressure-induced shifts and their temperature dependences in the ν₃ fundamental band of N₂O. The spectra used in this study were recorded using the 1-m McMath-Pierce Fourier transform spectrometer while it was located at the National Solar Observatory on Kitt Peak, AZ. Multispectrum analysis softwareD. C. Benner, C. P. Rinsland, V. Malathy Devi, M. A. H. Smith, D. Atkins, JQSRT 53 (1995) 705-721.as used to retrieve the line parameters using the Voigt and speed-dependent Voigt line profiles. The line mixing coefficients were calculated using the Exponential Power Gap scaling law. Comparisons with similar published results will be presented. D. C. Benner, C. P. Rinsland, V. Malathy Devi, M. A. H. Smith, D. Atkins, JQSRT 53 (1995) 705-721.w

Atmospheric isotopologues are useful tracers of dynamics and chemistry and can be used to constrain budgets of gases in the atmosphere. The Atmospheric Chemistry Experiment (ACE) routinely measures vertical profiles of over 35 molecules and 20 isotopologues via solar occultation from a satellite in low Earth orbit. The primary instrument is an infrared Fourier transform spectrometer with a spectral range of 750 – 4400 cm⁻¹and a resolution of 0.02 cm⁻¹. ACE began taking measurements in 2004 and is still active today. This talk focuses on isotopic measurements of CH₄, CO, CO₂, and N₂O from ACE-FTS. To complement ACE-FTS data, modeling using the Whole Atmosphere Community Climate Model (WACCM) was performed for each molecule.

ACE (also known as SCISAT) is making a comprehensive set of simultaneous measurements of numerous trace gases, thin clouds, aerosols and temperature by solar occultation from a satellite in low earth orbit. A high inclination orbit gives ACE coverage of tropical, mid-latitudes and polar regions. The primary instrument is a high-resolution (0.02 cm⁻¹) infrared Fourier Transform Spectrometer (FTS) operating in the 750-4400 cm⁻¹ region, which provides the vertical distribution of trace gases, and the meteorological variables of temperature and pressure. Aerosols and clouds are being monitored through the extinction of solar radiation using two filtered imagers as well as by their infrared spectra. After 14 years in orbit, the ACE-FTS is still operating well. A short introduction and overview of the ACE mission will be presented (see http://www.ace.uwaterloo.ca for more information). This talk will focus on recent ACE results and comparisons with chemical transport models.

The semi empirical MT_CKD model of the absorption continuum of water vapor is widely used in atmospheric radiative transfer codes of the atmosphere of Earth and exoplanets but lacks of experimental validation in the atmospheric windows. Recent laboratory measurements by Fourier transform Spectroscopy have led to self-continuum cross-sections much larger than the MT_CKD values in the near infrared transparency windows. In the present work, we report on accurate water vapor absorption continuum measurements by Cavity Ring Down Spectroscopy (CRDS) and Optical-Feedback-Cavity Enhanced Laser Spectroscopy (OF-CEAS) at selected spectral points of the transparency windows centered around 4.0, 2.1 and 1.25 μm. The temperature dependence of the absorption continuum at 4.38 μm and 3.32 μm is measured in the 23-39 ^°C range. The self-continuum water vapor absorption is derived either from the baseline variation of spectra recorded for a series of pressure values over a small spectral interval or from baseline monitoring at fixed laser frequency, during pressure ramps. In order to avoid possible bias approaching the water saturation pressure, the maximum pressure value was limited to about 16 Torr, corresponding to a 75% humidity rate. After subtraction of the local water monomer lines contribution, self-continuum cross-sections, C_S, were determined with a few % accuracy from the pressure squared dependence of the spectra base line level. Together with our previous CRDS and OF-CEAS measurements in the 2.1 and 1.6 μm windows, the derived water vapor self-continuum provides a unique set of water vapor self-continuum cross-sections for a test of the MT_CKD model in four transparency windows. Although showing some important deviations of the absolute values (up to a factor of 4 at the center of the 2.1 μm window), our accurate measurements validate the overall frequency dependence of the MT_CKD2.8 model.

NASA's Orbiting Carbon Observatory missions OCO-2 and OCO-3 require spectroscopic parameterization of the Oxygen A-Band absorption (757-775 nm) with unprecedented precision, to deliver space-based measurements of CO₂ column densities with an accuracy of better than 0.1%. Furthermore, with the long satellite-based pathlengths, the strongest A-Band lines are saturated. Accurate retrievals of O₂ column densities thus require precise modeling of the line shape, including the wings several linewidths from line center. The line shape model must go beyond the Voigt profile to include higher order effects such as Dicke narrowing, speed dependence, line mixing (LM), and collision-induced absorption (CIA). High precision laboratory data targeting these effects must be taken. Line mixing and collision induced absorption have proven to be especially problematic in satellite retrievals of O₂ column densities. LM and CIA are more prominent at lower temperatures and higher pressures. A temperature-stabilized photoacoustic spectrometer was therefore designed to study the temperature- and pressure-dependence of spectral line shapes at temperatures from 230-296 K and pressures up to 5 atm. Progress toward high resolution (2 MHz) measurements of the full A-Band will be presented. The observed lineshapes are analyzed with the Hartmann-Tran Profile (HTP), which incorporates LM and CIA , using the Labfit multispectrum fitting program, and the determination of LM and CIA effects will be presented.

Methylglyoxal is a known oxidation product of volatile organic compounds (VOCs) in Earth’s atmosphere. While the gas phase chemistry of methylglyoxal is fairly well understood, its modeled concentration and role in the formation of secondary organic aerosol (SOA) continues to be controversial. The gas phase hydration of methylglyoxal to form a gemdiol has been shown to occur in infrared studies but has not been widely considered for water-restricted environments such as the atmosphere. However, this process may have important consequences for the atmospheric processing or VOCs. We have recorded UV spectroscopic measurements following the hydration of methylglyoxal and have compared these measurements to calculated spectra of the electronic transitions of methylglyoxal and methylglyoxal diol. We will report on these measurements and discuss the implications for understanding the atmospheric processing and fate of methylglyoxal and similar molecules

Biogenic volatile organic compounds (BVOCs) are naturally occurring molecules that are emitted into the atmosphere by plants. BVOCs have an important role in atmospheric chemistry as they react readily with ozone, hydroxyl radicals, and nitric oxides to form aerosols and pollutants such as ozone in the troposphere. We are developing an IR spectrometer with the aim of measuring spectra of atmospheric samples of BVOCs to determine their concentrations. Using an external cavity quantum cascade laser (EC-QCL), we have acquired IR spectra of isoprene (C₅H₈) near 993 cm⁻¹. Isoprene represents an ideal target, as it is the simplest and most abundant BVOC. IR spectra of standard samples of isoprene were acquired in order to determine the detection limit of the spectrometer. We have also been working to improve the capabilities of the spectrometer by implementing wavelength modulation spectroscopy and increasing the path length through our samples by using a multipass cell. In this talk, we will present data from our initial measurements of the standard isoprene samples using a simple direct absorption setup as well as measurements using the improved spectrometer.