Hydroperoxide esters are important products in the class of reactions between Criegee intermediates and carboxylic acids. Such reactions are believed to play key roles in the formation of secondary organic aerosols by producing semivolatile and low-volatility organic compounds. We provide the first definitive evidence for the most fundamental reaction in this class, that between carbonyl oxide CH₂OO and formic acid HCOOH to form hydroperoxymethyl formate (HPMF), HOOCH₂OCHO. Using a modified continuous flow pulsed reactor, HPMF is characterized in the ozonolysis of ethylene by high resolution Fourier transform microwave spectroscopy. Evidence for the most stable conformer - a seven membered, hydrogen bond stabilized ring - is supported with high level calculations and observation of ¹³C isotopologues in natural abundance.

Dual frequency comb spectroscopy (DCS) is a rapidly evolving technique that provides a high-resolution, broadband spectrometer with no instrument lineshape and near perfect frequency calibrationCoddington I, Newbury N, Swann W. Dual-comb spectroscopy. Optica. 2016 Apr 20;3(4):414. These features make DCS well suited for accurate measurements of multiple species simultaneously. Because the frequency comb lasers can be well collimated, such a system can be used for long open-path measurements with path lengths ranging from hundreds of meters to several kilometers. Open-path measurements of atmospheric gas species over these path lengths are well suited to quantify emissions from sources like oil and gas, forest fires, and industry. Previous demonstrations of open-path DCS have primarily been in the 1-2 μm spectral region; however, in order to reach the sensitivity necessary to detect many atmospheric trace constituents, including volatile organic compounds, operation in the mid-infrared is required. Here, we show a mid-infrared open-path dual comb spectrometer operating in the 3-5 μm spectral region. We have used this spectrometer to measure methane, ethane, propane, and butane isomers (arising primarily from oil and gas activity) across a 1-km-long path in Boulder, CO for 1 week with an ethane sensitivity of  ∼ 0.1 ppb for a 2-minute time resolution. In addition, we show quantitative measurements of intentionally released acetone and isopropanol with a 1-σ sensitivity of 5.7 ppm · m and 2.4 ppm · m, respectively.

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Coddington I, Newbury N, Swann W. Dual-comb spectroscopy. Optica. 2016 Apr 20;3(4):414. .

A segmented Chirped Pulse Fourier Transform Microwave (CP-FTMW) spectrometer has recently been installed in the Molecular Photonics Laboratories at UNSW Sydney. It covers the K-band (18-26 GHz) with an 18 MHz per segment bandwidth. This frequency range permits probing samples at room temperature and in a supersonic expansion. The stable products of atmospheric oxidation reactions of biological and anthropogenic volatile organic carbons (VOCs) will probed in a room temperature cell. Reactive and transient species will be probed in a supersonic expansion using a custom discharge mixing nozzle. The nozzle combines a standard high voltage discharge source with a secondary source introduced into the expansion via a capillary gas line. This secondary source is pulsed to reduce gas load and improve sample density. Performance and preliminary results will be presented along with supporting ab initio calculations.

Fast spectral acquisition is an essential component in obtaining broadband molecular spectra with high signal to noise ratio, and in studying meta-stable molecular species. With the recent developments on commercially available arbitrary waveform generators (AWG), direct digital synthesizers (DDS), and room-temperature Schottky diodes, it is feasible now to perform fast spectroscopy scans using the heterodyne detection of the free induction decay of molecules in the millimeter wave bands, as demonstrated by a few pioneer spectrometer designs.E. Gerecht, K. O. Douglass and D. F. Plusquellic, 2011, Opt. Expr., 19, 8973; I. A. Finneran, D. B. Holland, P. B. Carrol et al., 2013, Rev. Sci. Instrum., 84, 083104.t Lille, we have developed and demonstrated the Fourier transform millimeter-wave (FTmmW) spectrometer system based on DDS.R. A. Motiyenko and L. Margulès, ISMS 73rd symposium (2018), WI07.his spectrometer has a simplified design which does not require external reference clocks or local oscillators, yet it achieves decent frequency resolution and high phase stability. Since then, several upgrades, including new frequency sweep scheme and filter applications, have been made to improve the spectral purity and scan bandwidth of this FTmmW system. The results of the detailed performance test of bandwidth, sensitivity and data acquisition rate on the upgraded system will be presented. The advantages and limitations of the spectrometer for conducting fast millimeter spectroscopy on atmospheric radicals will be discussed. The authors thank the Région Hauts-de-France, and the Ministère de l’Enseignement Supérieur et de la Recherche (CPER Climibio), the French ANR Labex CaPPA through the PIA (contract ANR-11-LABX-0005-01), and the European Fund for Regional Economic Development for their financial support.

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E. Gerecht, K. O. Douglass and D. F. Plusquellic, 2011, Opt. Expr., 19, 8973; I. A. Finneran, D. B. Holland, P. B. Carrol et al., 2013, Rev. Sci. Instrum., 84, 083104.A R. A. Motiyenko and L. Margulès, ISMS 73rd symposium (2018), WI07.T

Methoxyphenol (MP) are biogenic volatile organic compounds which contribute significantly to biomass burning emissions. MP compounds are able to chemically evolve in the atmosphere and several studies aimed to determine the kinetics and the reactivity intermediates involved in the tropospheric oxidation processes and the subsequent production of secondary organic aerosols whose impact to the climate seems to be decisive.[1] The gas phase monitoring of MP in the atmosphere requires precise rovibrational cross-sections measurements which can be accurately simulated only if the rotational structures both in the vibrational ground state (GS) and excited states (ES) are understood. Recent rotational studies reported about ortho (2-MP), meta (3-MP) and para (4-MP) isomers enabled to characterize their conformational landcape from GS rotational and quartic centrifugal constants to reproduce the millimeter-wave spectra at the experimental accuracy.[2,3] Any vibrational spectrum of MP compounds resolved in rotation could not be recorded so far, mainly due both to the presence of hot bands and to the complexity of the conformational landscape. Taking advantage of our tunable quantum cascade laser spectrometer coupled to a pulsed slit jet [4] we recorded the infrared spectrum of the ν₁₈ ring in plane bending mode of the 3-MP isomer around 950 cm⁻¹. Rovibrational analyses supported by the full characterization of the conformational landscape in the GS state [2] provide for the first time unambiguous infrared signatures of two out of four possible conformers of 3-MP including a reliable set of ES rotational constants. A more extensive study in the region of CC ring stretching modes is currently in progress to resolve the four conformational signatures of 3-MP and to bring new insights about the conformational flexibility of these compounds. References : [1] A. Lauraguais et al. Atm. Envir. 86, 155-163 (2014).[2] A. Roucou et al. CPC 19, 1-8 (2018). [3] A. Jabri et al., accepted in JCP (2019). [4] P. Asselin et al. PCCP 19, 17224-17232 (2017).

Widespread deployment (both ground-based and spaceborne) of millimeter/submillimeter radiometers for composition specific atmospheric retrievals has been hindered by the cost, complexity, and power requirements traditionally associated with this hardware. One possible avenue to make such measurements more routine are millimeter-wave (180-200 GHz) heterodyne-detection electronics fabricated with complementary metal-oxide semiconductor (CMOS) process techniques. When outfitted with indium phosphide (InP) low-noise amplifier (LNA) stages, cryogen free system temperatures (T_sys) of 800 - 1000 K can be achieved. This receiver system has been equipped with with a custom 6GS/s ADC / FFT (3GHz bandwidth) system-on-chip to spectrally disperse the generated intermediate frequency signal to allow for composition specific measurements of gas-phase samples.Y. Kim et al., "A 183-GHz InP/CMOS-Hybrid Heterodyne-Spectrometer for Spaceborne Remote Sensing," IEEE Trans. THz Sci. Technol., In Review.he resulting system can be configured to meet the stringent size and power requirements needed for CubeSat/SmallSat integration thus making for a potentially useful planetary science instrument (i.e., limb sounder). This talk will discuss the performance properties of all components, laboratory trails demonstrating sensitivity to rarefied samples of CH₃CN and H₂O, and future plans for field deployment on ground-based and stratospheric balloon platforms.

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Y. Kim et al., "A 183-GHz InP/CMOS-Hybrid Heterodyne-Spectrometer for Spaceborne Remote Sensing," IEEE Trans. THz Sci. Technol., In Review.T

The recent use of bromomethyl radical as a novel precursor for producing the simplest Criegee intermediates (CH₂OO) motivates our high-resolution investigation of CH₂Br. Cold CH₂Br (rotational temperature of 20 K) is generated by seeding CH₂Br₂ into a Ne/He pulsed supersonic slit-jet discharge expansion. Sub-Doppler infrared absorption in the CH₂ symmetric stretch band is fully resolved at high single-to-noise ratio, yielding band origins measured at 3052.9781 ±0.0004  cm⁻¹ for CH₂   ⁷⁹Br and 3052.9775 ±0.0004  cm⁻¹ for CH₂   ⁸¹Br, respectively. The rotationally resolved structure is fitted to a non-rigid rotor Hamiltonian with spin-rotation coupling, furnishing rotational constants and the spin-orbit coupling tensor for the vibrationally excited state. The results are consistent with a vibrationally averaged planar π radical with unpaired electron spin density in a partially filled p_π-orbital on the central carbon atom. These measurements complete the set of high-resolution investigations of the symmetric-stretch mode for mono-halogen substituted methyl radicals (CH3X, X = F, Cl, Br, I). We use this opportunity to examine trends in molecular properties with variation of the substituent halogen atom, for example, regarding vibrationally averaged geometries and symmetric stretch band origins. A combination band is also analyzed, likely originating from the lowest-energy, out-of-plane vibrational bending mode. Evidence of hyperfine structure is observed as well. Interestingly, despite high signal to noise on the symmetric CH stretch vibrational mode, we find no evidence for the asymmetric CH stretch spectrum at our current sensitivities, which we interpret as resulting from strong enhancement of the symmetric stretch band by vibrationally mediated "charge-sloshing" dynamics in the C-Br bond.

r0pt Figure Volcanoes reject large amounts of sulfur-containing gases in the atmosphere; these represent 10 to 15 % of the anthropogenic sulfur emissions. Thermodynamic considerations show that silicon tetrafluoride (SiF₄) should be a normal trace component of volcanic gases. Some studies report that the possible importance of SiF₄ had been neglected because of the problems of reporting HF and SiF₄ separately in conventional analyses. However, a better knowledge of spectroscopic parameters is needed for this molecule in order to derive accurate concentrations. This is why we undertook an extensive high-resolution study of its infrared absorption bands, including the fundamentals and several overtone and combinations. We present here a detailed analysis and modeling of the strongly absorbing ν₃ fundamental, for the there isotopplogues in natural abundance: ²⁸SiF₄ (92.23 %), ²⁹SiF₄ (4.67 %) and ³⁰SiF₄ (3.10 %). Progresses in the analysis of the other bands will be outlined.

The sulphur-monoxide B ³Σ⁻(v ≥ 4) levels are known to be strongly affected by vibrationally-dependent predissociation and local energy perturbations (Liu et al. 2006 JMS 238:213). The isotope-dependence of this predissociation and the SO photodissociation cross section is a candidate atmospheric-source for explaining the anomalous ³²S/³³S/³⁴S/³⁶S isotopic fractionation found in 2.5Ga old sedimentary material (Ono 2017 Annu. Rev. Earth Pl. Sc. 45:301). We have recorded new photoabsorption spectra between 195 and 230 nm to determine spectroscopic constants, predissociation linewidths, and transition strengths for the excited B ³Σ⁻(v=4−17) levels of ³²S¹⁶O, ³³S¹⁶O, and ³⁴S¹⁶O. The C ³Π state is also observed and perturbs B ³Σ⁻(v=4−17) through spin-orbit interaction. B ³Σ⁻ and C ³Π potential-energy curves, electronic transition moments, and a global spin-orbit interaction are deduced from the new data so that it may be extrapolated to the rare ³⁶S¹⁶O isotopologue. We use the new cross sections to explore the potential for isotope-dependent photodissociation of SO in the ancient-Earth atmosphere due to structured solar UV radiation and atmospheric opacity.