Sulfur compounds have been observed in the atmospheres of a number of planetary bodies in our solar system including Venus, Earth, Mars, Io, Europa, and Callisto. The global cloud cover on Venus located at an altitude between 50 and 80 kilometers is composed primarily of sulfuric acid (H₂SO₄) and water. Planetary photochemical models have attempted to explain observations of sulfuric acid and sulfur oxides with significant discrepancies remaining between models and observation. In particular, high SO₂ mixing ratios are observed above 90 km which exceed model predictions by orders of magnitude. Work recently done in the Vaida lab has shown red light can drive photochemistry through overtone pumping for acids like H₂SO₄ and has been successful in explaining much of the sulfur chemistry in Earth’s atmosphere. Water can have a number of interesting effects such as catalysis, suppression, and anti-catalysis of thermal and photochemical processes. We investigate the role of water complexes in the hydration of sulfur oxides and dehydration of sulfur acids and present spectroscopic studies to document such effects. We investigate these reactions using FTIR and UV/Vis spectroscopy and will report on our findings.

The arrival of the Cassini spacecraft in orbit around Saturn has led to the discovery of benzene at ppm levels, as well as large positive ions evocative of polycyclic aromatic hydrocarbons (PAHs) in Titan’s atmosphere. Recently, the assignment of the band at 3.28 μm as observed by the Visual–Infrared Mapping Spectrometer (VIMS) to gas-phase PAHs provides further evidence that these molecules are prevalent on Titan. These observations suggest that aromatic reaction pathways play an important role in the photochemistry of Titan’s atmosphere, in particular in the formation of large organic species. These aerosols eventually settle out of the atmosphere onto the surface of Titan giving rise to the different surface albedos that are observed by the VIMS instrument onboard Cassini. We will present results from a laboratory study of the UV irradiation of ppm-level aromatic precursors to understand their influence on the observable characteristics of Titan’s surface. Spectroscopic measurements of our analog aerosols compare favorably to observations of Titan’s haze by VIMS and by the Composite Infrared Spectrometer (CIRS) in the far-infrared. In addition, the broad aerosol emission feature centered at approximately 145 cm⁻¹is of particular interest. From the broadness of this feature, we speculate that the emission is a blended composite of low-energy vibrations of large molecules such as polycyclic aromatic hydrocarbons (PAHs) and their nitrogen containing counterparts, polycyclic aromatic nitrogen heterocycles (PANHs). A further comparison of our aerosol spectra to the surface observations carried out by Cassini also shows a strong correlation between the aerosol makeup and the surface albedo of Titan. Using laser desorption mass spectrometry (LDMS) and collision-induced dissociation (CID) MS/MS techniques we confirm the presence of large (5+ rings) PAHs/PANHs in our aerosols and discuss possible formation pathways.

We have recorded high-resolution (FWHM = 0.2 Å) extreme-ultraviolet (EUV, 800-1350 Å) laboratory emission spectra of molecular nitrogen excited by 20 and 100 eV electron impact under mostly optically thin conditions. From these, emission cross sections were determined for a total of 491 features arising from N₂ electronic-vibrational transitions and atomic N I and N II multiplets. Molecular emission was observed from those excited levels which are not completely predissociative and to ground-state vibrational levels as high as v=17. The frequently-blended molecular emission bands were disentangled with the aid of a coupled-channels model of excited N₂ states that includes the strong coupling between valence and Rydberg electronic states and the effects of predissociation. The observed emission bands probe a large range of vibrational motion so that internuclear-distance-dependent electronic transition moments could be deduced experimental. The coupled-channels model could then be used to predict the emission cross sections of unobserved bands and those that are optically thick in the experimental spectra. The electron-impact-induced fluorescence measurements and model were compared with Cassini UVIS observations of emissions from Titan's upper atmosphere.

In the interstellar medium, as well as in icy comets, ammonia may be a crucial species in the first step toward the formation of amino-acids and other prebiotic molecules such as hydroxylamine (NH₂OH). It is worth to notice that the NH₃/H₂ ratio in the ISM is 3 10⁻⁵ compared the H₂O/H₂ one which is only 7 10⁻⁵. Using either electron-UV irradiations of water-ammonia ices or successive hydrogenation of solid nitric oxide, laboratory experiments have already shown the feasibility of reactions that may take place on the surface of ice grains in molecular clouds, and may lead to the formation of this precursor. Herein is proposed a new reaction pathway involving ammonia and hydroxyl radicals generated in a microwave discharge. Experimental studies, at 3 and 10 K, in solid phase as well as in neon matrix have shown that this reaction proceed via a hydrogen abstraction, leading to the formation of NH₂ radical, that further recombine with hydroxyl radical to form hydroxylamine, under non-energetic conditions.

High-resolution infrared absorption spectra have been created for the ν₉ band of ethane (C₂H₆) at 823 cm⁻¹using the Fourier transform spectrometer at the Australian Synchrotron . Infrared spectra were recorded at four different pressures for four temperatures (200, 160, 120 and 90 K) relevant to typical conditions on Titan. The THz/Far-IR beamline at the Australian Synchrotron is unique in combining a high-resolution Fourier transform spectrometer with an `enclosive flow cooled' (EFC) cell designed to study gas phase molecules at low temperatures. The low vapor pressure of ethane at 90 K means that the EFC cell is necessary to obtain high-resolution spectra. Our cross sections and line parameters are needed to improve retrievals of ethane on Titan.

We have measured^a over 130 pure rotational transitions of the lowest torsional state, ν₁₈, of C₂H₅D using a double pass 3 meter cell held at 0.2 Torr of sample pressure in the frequency ranges of 540-600, 680-800 and 940-1080 GHz. The program ERHAM^b, Effective Rotational Hamiltonian Method, was used to construct the Hamiltonian that included ρ, ϵ₁, β, 9 rotational and centrifugal distortion constants and 8 torsional constants. Fitted values of ϵ₁ = 1127.82(35) MHz, ρ = 0.4342 MHz and β = 1.317(22) MHz enable predictions to experimental accuracy of both a and b-dipole allowed pure rotational transitions which have A - E splittings of 70 MHz and 1.3 GHz respectively. The data, combined with ground state data, will be useful to derive information regarding the potential barrier to internal rotation. This analysis supports our ongoing work to assign the infrared spectrum in the 700-900 cm⁻¹ region to enable the first detection in outer planet atmospheres. ^aResearch described in this paper was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contracts and cooperative agreements with the National Aeronautics and Space Administration. ^bP. Groner J. Mol. Spec. 278 (2012) 52-67.

High-resolution, high signal-to-noise spectra of mono-substituted ¹³C-ethane (¹³C¹²CH₆) in the 12.2 μm region were recorded with a Bruker IFS 125HR Fourier transform spectrometer. The spectra were obtained for four sample pressures at three different temperatures between 130 and 208 K using a 99% ¹³C-enriched ethane sample contained in a 20.38-cm long coolable absorption cell¹. A multispectrum nonlinear least squares fitting technique² was used to fit the same intervals in the four spectra simultaneously to determine line positions and intensities. Similar to our previous analyses of ¹²C₂H₆ spectra in this same region³, constraints were applied to accurately fit each pair of doublet components arising from torsional Coriolis interaction of the excited ν₁₂ = 1 state with the nearby torsional ν₆ = 3 state. Line intensities corresponding to each spectrum temperature (130 K, 178 K and 208 K) are reported for 1660 ν₁₂ absorption lines for which the assignments are known, and integrated intensities are estimated as the summation of the measured values. The measured line positions and intensities (re-scaled to 296 K) are compared with values in recent editions of spectroscopic databases.⁴
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¹K. Sung, A. W. Mantz, L. R. Brown, et al., J. Mol. Spectrosc. 162 (2010) 124-134. ²D. C. Benner, C. P. Rinsland, V. Malathy Devi, M. A. H. Smith and D. Atkins, JQSRT 53 (1995) 705-721. ³V. Malathy Devi, C. P. Rinsland, D. Chris Benner, et al., JQSRT 111 (2010) 1234-1251; V. Malathy Devi, D. Chris Benner, C. P. Rinsland, et al., JQSRT 111 (2010) 2481-2504. ⁴Research described in this paper was performed at Connecticut College, the College of William and Mary, NASA Langley Research Center and the Jet Propulsion Laboratory, California Institute of Technology, under contracts and cooperative agreements with the National Aeronautics and Space Administration.

Propyne (CH₃-C ≡ CH) is an important molecule in astrophysics and planetary atmospheres, and an important constituent of fuels. Spectroscopic investigation of propyne is also of fundamental interest in intramolecular vibrational redistribution (IVR) dynamics of hydrocarbons. Although extensive spectroscopic studies on this simple organic molecule have been performed, the ν₃+ν₈ band has not been reported before. In this presentation, the high-resolution infrared spectrum of the ν₃+ν₈ combination band of propyne is presented.¹ Continuous-wave cavity ring-down spectroscopy is used to measure this weak infrared band in the 3175 cm⁻¹ region using a supersonic free jet. The rotational analysis of the experimental spectrum results in accurate spectroscopic parameters for the ν₃+ν₈ combination vibrational state. Severe perturbations are found for K = 3 and 4 rotational levels, and are likely due to near-resonant or non-resonant interactions between the ν₃+ν₈ and other vibrational states. Moreover, three parallel-transition type subbands are observed and their analysis is presented as well.
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¹D. Zhao, H. Linnartz, Chem. Phys. Lett. (2014), DOI: 10.1016/j.cplett.2014.02.016.

In the past few decades, many high-resolution spectroscopic studies have been dedicated to the C-H stretch vibrations in propyne (CH₃-C ≡ CH), aiming to understand the intramolecular vibrational redistribution in isolated small hydrocarbons. In this talk, we present the sensitive detection of the ν₁ (acetylenic C-H stretch) fundamental bands of the three ¹³C mono-substituted isotopologues of propyne. The infrared absorption spectra are recorded using continuous-wave cavity ring-down spectroscopy (CRDS) in combination with a supersonic jet expansion of propyne/argon gas mixtures. A 0.05x30 mm slit nozzle is used in the present experiment to realize an effective rotational cooling to ≈ 14 K and a reduced Doppler width of ≈ 90 MHz. The high sensitivity of CRDS allows us to detect the three ¹³C isotopologues in their 1.1% natural abundance. Different infrared band intensities of ν₁ are found for the three isotopologues. Detailed rotational analyses of the experimental spectra are performed to derive effective spectroscopic constants for the upper ν₁ vibrational state. The ¹³C-substitution effect of the near/non-resonant perturbations to ν₁ of propyne is discussed. In addition, more accurate infrared data of ¹²C-propyne, including the ν₁ fundamental band, are also obtained from our experimental spectra.

Titan’s stratosphere is abundant in hydrocarbons (C_xH_y) producing highly complicated and crowded features in the spectra of Cassini/CIRS. Among these, benzene (C₆H₆) is the heaviest hydrocarbon ever seen in the Titan and cold planets. For this reason, a series of pure and N₂-broadened C₆H₆ spectra were recorded in the 640 to 1540 cm⁻¹region at gas temperatures down to 231 K using a Fourier transform spectrometer (Bruker IFS-125HR) at the Jet Propulsion Laboratory. We report temperature dependent absorption cross sections for three strong fundamental bands (ν₄, ν₁₄, ν₁₃). We also derived pseudo-line parameters, which include mean intensities and effective lower state energies on a 0.005 cm⁻¹frequency grid, obtained by fitting all the laboratory spectra simultaneously. For the pseudoline generation, details can be found in a JPL MK-IV website, http://mark4sun.jpl.nasa.gov/data/spec/Pseudo). The resulting pseudolines of the strong bands reproduce observed cross sections to within ~3 %. These new results are compared to earlier work, including the C₆H₆+N₂ spectra recorded at PNNL.^{1 2}
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¹S. W. Sharpe, et al., Appl Spectrosc 58, 1452-1461 (2004); C. P. Rinsland, et al. JQSRT, 109, 2511-2522 (2008). ²Research described in this paper was performed at the Jet Propulsion Laboratory and California Institute of Technology, under contracts and cooperative agreements with the National Aeronautics and Space Administration.

The atmosphere of Titan contains nitrogen, methane, and a rich mixture of more complex hydrocarbons and nitriles produced by photochemical processing. Data from the 2005 Cassini-Huygens mission suggests that among the more complex compounds are substituted benzenes that are themselves precursors to large polymeric tholins.¹ Nitriles are particularly prevalent in Titan’s atmosphere due to the dominance of N₂ in the atmosphere. The cyanostyrenes are of particular interest, in part because they have the same molecular formula (C₉H₇N) as quinoline, a prototypical heteroaromatic, and therefore could engage in photochemical isomerization to form this molecule of significant pre-biotic relevance. As a first step in understanding the pathways leading to heteroaromatics, we have studied the isotope-selective spectroscopy of o-,m-, and p-cyanostyrene under jet-cooled conditions relevant to Titan’s atmosphere. In this talk, the excitation and emission spectra for the three isomers will be presented. Using a combination of resonant two-photon ionization, LIF excitation, and dispersed fluorescence spectroscopies, the vibronic spectroscopy of the three isomers were recorded and compared. The meta isomer has two conformational isomers, which have been distinguished and studied using hole-burning methods. The talk will compare and contrast the UV spectral signatures of the set of structural and conformational isomers of the cyanostyrenes, using the ethynylstyrene counterparts as points of comparison.²
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¹Sebree, J. A.; Kidwell, N. M.; Selby, T. M.; Amberger, B. K.; McMahon, R. J.; Zwier, T. S., Photochemistry of Benzylallene: Ring-Closing Reactions to Form Naphthalene. Journal of the American Chemical Society 2012, 134 (2), 1153-1163. ²Selby, T. M.; Clarkson, J. R.; Mitchell, D.; Fitzpatrick, J. A. J.; Lee, H. D.; Pratt, D. W.; Zwier, T. S., Isomer-Specific Spectroscopy and Conformational Isomerization Energetics of o-, m-, and p-Ethynylstyrenes. The Journal of Physical Chemistry A 2005, 109 (20), 4484-4496.