Acetoin, CH₃C(O)CH(OH)CH₃, is an additive used in foods and cigarettes as well as a common component of biomass pyrolysate during the production of biofuels, yet little is known about its thermal decomposition mechanism. In order to identify thermal decomposition products of acetoin, a gas-phase mixture of approximately 0.3% acetoin in argon was subject to pyrolysis in a resistively heated SiC microtubular reactor at 1100-1500 K. Matrix-isolation FTIR spectroscopy was used to identify pyrolysis products. Many products were observed in analysis of the spectra, including acetylene, propyne, ethylene, and vinyl alcohol. These results provide clues to the overall mechanism of thermal decomposition and are important for predicting emissions from many industrial and residential processes.

Ball plasmoids (self-sustaining spherical plasmas) are a particularly unique example of a non-equilibrium air plasma. These plasmoids have lifetimes on the order of hundreds of milliseconds without an external power source, however, current models dictate that a ball plasmoid should recombine in a millisecond or less. Ball plasmoids are considered to be a laboratory analogue of natural ball lightning, a phenomenon that has eluded scientific explanation for centuries. We are searching for the underlying physicochemical mechanism(s) by which ball plasmoids and (by extension) ball lightning are stabilized using a variety of diagnostic techniques. This presentation will focus on optical emission spectroscopy (OES) of ball plasmoid discharges between 190-850 nm. The previous generation of OES measurementsVersteegh, A.; Behringer, K.; Fantz, U.; Fussman, G.; Jüttner, B.; Noack, S. Plas. Sour. Sci. Technol. 2008, 17(2), 024014^,Stephan, K. D.; Dumas, S.; Komala−Noor, L.; McMinn, J. Plas. Sour. Sci. Technol. 2013, 22(2), 025018f this system showed emission from only a few atomic and molecular species, however, the energy available for the discharges in these experiments was limited by the size of the capacitor banks and voltages to which the capacitor banks were charged. We are capable of generating plasmoids at much higher energies, and as a result we are the first to report a very rich chemistry previously not observed in ball plasmoids. We have identified signals from species including NO A^2

Σ

^+

→X2

, OH A^2

Σ

^+

→X2

, NH A^3

Π

X^3

Σ

^-, AlO A^2

Π

X^2

Σ

^+, NH^+ B^2

∆

X^2

The biological importance of nitric oxide has been known for nearly forty years due to its role in cardiovascular and nervous signaling. The main carrier molecules, s-nitrosothiols (RSNOs), are of additional interest due to their role in signaling reactions. Additionally, these compounds are related to several diseases including muscular dystrophy, stroke, myocardial infarction, Alzheimer's disease, Parkinson's disease, cystic fibrosis, asthma, and pulmonary arterial hypertension. One of the main barriers to elucidating the role of these RSNOs is the low (nanomolar) concentration present in samples of low volume (typically  ∼ 100 μL). To this end we have set up a cavity ring-down spectrometer tuned to observe ¹⁴NO and ¹⁵NO released from cell growth samples. To decrease the limit of detection we have implemented a laser locking scheme employing Zeeman modulation of NO in a reference cell and have tuned the polarization of the laser using a half wave plate to optimize the polarization for the inherent birefringence of the CRDS mirrors. Progress toward measuring RSNO concentration in biological samples will be presented.

Radiocarbon (¹⁴C) dating of organic materials is based on measuring the ¹⁴C/¹²C atomic fraction relative to the nascent value that existed when the material was formed by photosynthetic conversion of carbon dioxide present in the atmosphere. This field of measurement has numerous applications including source apportionment of anthropogenic and biogenic fuels and combustion emissions, carbon cycle dynamics, archaeology, and forensics. Accelerator mass spectrometry (AMS) is the most widely used method for radiocarbon detection because it can measure extremely small amounts of radiocarbon (background of nominally 1.2 parts-per-trillion) with high relative precision (0.4 %). AMS measurements of radiocarbon are typically calibrated by reference to standard oxalic-acid (C₂H₂O₄) samples of known radiocativity that are derived from plant matter. Specifically, the internationally accepted absolute dating reference for so-called "modern-equivalent" radiocarbon is 95 % of the specific radioactivity in AD 1950 of the National Bureau of Standards (NBS) oxalic acid standard reference material and normalized to δ¹³C_VPDB = 19 per mil M. Stuiver and H. A. Polach, Radiocarbon 19, (1977) 355. With this definition, a "modern−equivalent" corresponds to 1.176(70) parts−per−trillion of ^14C relative to total carbon content.As an alternative radiocarbon scale, we propose an SI−traceable method to determine ^14C absolute concentration which is based on linear Beer−Lambert−law absorption measurements of selected ^14C^16O_2 _3−band line areas. This approach is attractive because line intensities of chosen radiocarbon dioxide transitions can be determined by ab initio calculations with relative uncertainties below 0.5 %. This assumption is justified by the excellent agreement between theoretical values of line intensities and measurements for stable isotopologues of CO_2 O. L. Polyansky et al., Phys. Rev. Lett. 114, (2015) 243001. In the case of cavity ring-down spectroscopy (CRDS) measurements of ¹⁴C¹⁶O₂ peak areas, we show that absolute, SI-traceable concentrations of radiocarbon can be determined through measurements of time, frequency, pressure and temperature. Notably, this approach will not require knowledge of the radiocarbon half-life and is expected to provide a stable scale that does not require an artifact standard.

---

Footnotes:

M. Stuiver and H. A. Polach, Radiocarbon 19, (1977) 355\end O. L. Polyansky et al., Phys. Rev. Lett. 114, (2015) 243001

The thermal lens technique is applied to vibrational overtone spectroscopy of solutions of naphthalene in n-hexane. The pump and probe thermal lens technique is found to be very sensitive for detecting samples of low composition (ppm) in transparent solvents. In this experiment two different probe lasers: one at 488 nm and another 568 nm were used. The C-H fifth vibrational overtone spectrum of benzene is detected at room temperature for different concentrations. A plot of normalized integrated intensity as a function of concentration of naphthalene in solution reveals a non-linear behavior at low concentrations when using the 488 nm probe and a linear behavior over the entire range of concentrations when using the 568 nm probe. The non-linearity cannot be explained assuming solvent enhancement at low concentrations. A two color absorption model that includes the simultaneous absorption of the pump and probe lasers could explain the enhanced magnitude and the non-linear behavior of the thermal lens signal. Other possible mechanisms will also be discussed.

Imidazolium based ionic liquids (ILs) have been used as a promising system to improve the CO₂ electroreduction at lower overpotential than other organic or aqueous electrolytes¹. Although the detailed mechanism of the CO₂ electroreduction on Ag has not been elucidated yet, we have developed a methodology to study the electrified interface during the CO₂ electroreduction using sum frequency generation (SFG) spectroscopy in combination with cyclic voltammetry². In this work, we tuned the composition of imidazolium-based ILs by exchanging the anion or the functional groups of the imidazolium. We use the nonresonant SFG (NR-SFG) to study the IL-Ag interface and resonant SFG (RES-SFG) to identify the CO adsorbed on the electrode and monitor the Stark shift as a function of cell potential. In previous studies on CO₂ electroreduction in the IL: 1-ethyl-3-methylimidazolium tetrafluorborate (EMIM-BF₄) on Ag, we showed three events occurred at the same potential (-1.33 V vs. Ag/AgCl): the current associated with CO₂ electroreduction increased, the Stark shift of the adsorbed atop CO doubled in magnitude and the EMIM-BF₄ underwent a structural transition³. In addition, we also observed how the structural transition of the EMIM-BF₄ electrolyte shift to lower potentials when the IL is mixed with water. It is known that water enhances the CO₂ electroreduction producing more CO⁴. Moreover, the CO is adsorbed in multi-bonded and in atop sites when more water is present in the electrolyte. ¹Lau, G. P. S.; Schreier, M.; Vasilyev, D.; Scopelliti, R.; Grätzel, M.; Dyson, P. J., New Insights into the Role of Imidazolium-Based Promoters for the Electroreduction of CO₂ on a Silver Electrode. J. Am. Chem. Soc. 2016, 138, 7820-7823. ²García Rey, N.; Dlott, D. D., Studies of Electrochemical Interfaces by Broadband Sum Frequency Generation. J. Electroanal. Chem. 2016. DOI:10.1016/j.jelechem.2016.12.023. ³García Rey, N.; Dlott, D. D., Structural Transition in an Ionic Liquid Controls CO₂ Electrochemical Reduction. J. Phys. Chem. C 2015, 119, 20892–20899. ⁴Rosen, B. A.; Zhu, W.; Kaul, G.; Salehi-Khojin, A.; Masel, R. I., Water Enhancement of CO₂ Conversion on Silver in 1-Ethyl-3-Methylimidazolium Tetrafluoroborate. J. Electrochem. Soc. 2013, 160, H138-H141.

With the advancement of chirped-pulse techniques, broadband rotational spectra with a few tens to several hundred GHz of spectral coverage are now routinely recorded. When studying multi-component mixtures that might result, for example, with the use of an electrical discharge, lines of new chemical species are often obscured by those of known compounds, and analysis can be laborious. To address this issue, we have developed SPECdata, an open source, interactive tool which is designed to simplify and greatly accelerate the spectral analysis and discovery. Our software tool combines both automated and manual components that free the user from computation, while giving him/her considerable flexibility to assign, manipulate, interpret and export their analysis. The automated - and key - component of the new software is a database query system that rapidly assigns transitions of known species in an experimental spectrum. For each experiment, the software identifies spectral features, and subsequently assigns them to known molecules within an in-house database (Pickett .cat files, list of frequencies...), or those catalogued in Splatalogue (using automatic on-line queries). With suggested assignments, the control is then handed over to the user who can choose to accept, decline or add additional species. Data visualization, statistical information, and interactive widgets assist the user in making decisions about their data. SPECdata has several other useful features intended to improve the user experience. Exporting a full report of the analysis, or a peak file in which assigned lines are removed are among several options. A user may also save their progress to continue at another time. Additional features of SPECdata help the user to maintain and expand their database for future use. A user-friendly interface allows one to search, upload, edit or update catalog or experiment entries.

A typical broadband rotational spectrum may contain several thousand observable transitions, spanning many species Perez et al. “Broadband Fourier transform rotational spectroscopy for structure determination: The water heptamer.” Chem. Phys. Lett., 2013, 571, 1–15. Identifying the individual spectra, particularly when the dynamic range reaches 1,000:1 or even 10,000:1, can be challenging. One approach is to apply automated fitting routinesSeifert et al. “AUTOFIT, an Automated Fitting Tool for Broadband Rotational Spectra, and Applications to 1-Hexanal.” J. Mol. Spectrosc., 2015, 312, 13–21. In this approach, combinations of 3 transitions can be created to form a “triple”, which allows fitting of the A, B, and C rotational constants in a Watson-type Hamiltonian. On a standard desktop computer, with a target molecule of interest, a typical AUTOFIT routine takes 2–12 hours depending on the spectral density. A new approach is to utilize machine learningBishop. “Neural networks for pattern recognition.” Oxford university press, 1995.o train a computer to recognize the patterns (frequency spacing and relative intensities) inherit in rotational spectra and to identify the individual spectra in a raw broadband rotational spectrum. Here, recurrent neural networks have been trained to identify different types of rotational spectra and classify them accordingly. Furthermore, early results in applying convolutional neural networks for spectral object recognition in broadband rotational spectra appear promising.

---

Footnotes:

Perez et al. “Broadband Fourier transform rotational spectroscopy for structure determination: The water heptamer.” Chem. Phys. Lett., 2013, 571, 1–15.. Seifert et al. “AUTOFIT, an Automated Fitting Tool for Broadband Rotational Spectra, and Applications to 1-Hexanal.” J. Mol. Spectrosc., 2015, 312, 13–21.. Bishop. “Neural networks for pattern recognition.” Oxford university press, 1995.t

Advances in chemical sensitivity and robust, solid-state designs for microwave/millimeter-wave instrumentation compel the expansion of molecular rotational spectroscopy as research tool into applied science. It is familiar to consider molecular rotational spectroscopy for air analysis. Those techniques for molecular rotational spectroscopy are included in our presentation of a more broad application space for materials analysis using Fourier Transform Molecular Rotational Resonance (FT-MRR) spectrometers. There are potentially transformative advantages for direct gas analysis of complex mixtures, determination of unknown evolved gases with parts per trillion detection limits in solid materials, and unambiguous chiral determination. The introduction of FT-MRR as an alternative detection principle for analytical chemistry has created a ripe research space for the development of new analytical methods and sampling equipment to fully enable FT-MRR. We present the current state of purpose-built FT-MRR instrumentation and the latest application measurements that make use of new sampling methods.

Microwave spectroscopy has been a proven technique for the detection of short-lived molecules produced from a variety of molecular sources. With the goal of observing more reactive intermediates produced in combustion reactions, the products of a home-built flat flame burner were measured on a coaxially oriented beam resonator arrangement (COBRA) Fourier transform microwave spectrometer.J.-U. Grabow, W. Stahl, H. Dreizler, Rev. Sci. Instrum. 67, 4072, 1996he products are coupled into a molecular beam using a fast-mixing nozzle styled after the work of Gutowsky and co-workers.T. Emilsson, T. D. Klots, R. S. Ruoff, H.S. Gutowsky, J. Chem. Phys. 93, 6971, 1990robing the flame at various positions, the relative abundance of products can be observed as a function of flame depth. One dimensional intensity profiles are available for formaldehyde, ketene, acetaldehyde, and dimethyl ether, where either a dimethyl ether fuel or an ethylene fuel was burned in the presence of oxygen. The current arrangement allows only for stable species produced in the flame to be observed in the molecular beam. This combination of species source and detection shows promise for future work in observing new, short-lived, combustion intermediates.

---

Footnotes:

J.-U. Grabow, W. Stahl, H. Dreizler, Rev. Sci. Instrum. 67, 4072, 1996T T. Emilsson, T. D. Klots, R. S. Ruoff, H.S. Gutowsky, J. Chem. Phys. 93, 6971, 1990P

Microwave spectroscopy can uniquely identify molecules because their rotational energy levels are sensitive to the three principal moments of inertia. However, a priori predictions of a molecule's structure have traditionally been required to enable efficient assignment of the rotational spectrum. Recently, automated microwave double resonance spectroscopy (AMDOR) has been employed to rapidly generate two dimensional spectra based on transitions that share a common rotational level, which may enable automated extraction of rotational constants without any prior estimates of molecular structure. Algorithms used to date for AMDOR have relied on making several initial assumptions about the nature of a subset of the linked transitions, followed by testing possible assignments by “brute force.” In this talk, we will discuss new strategies for interpreting AMDOR spectra, using eugenol as a test case, as well as prospects for library-free, automated identification of the molecules in a volatile mixture.