We have generated NO₃ from pyrolysis of N₂O₅ following supersonic free jet expansion, and carried out two color resonant four wave mixing ( 2C-R4WM ) spectroscopy of the B̃ ²E′ - X̃ ²A₂′ electronic transition. One laser was fixed to pump NO₃ to a ro-vibronic level of the B̃ state, and the other laser ( probe ) was scanned across two levels of the X̃ ²A₂′ state lying at 1051 and 1492 cm⁻¹, the ν₁ (a₁′) and ν₃ (e′) fundamentals, respectively. The 2C-R4WM spectra have unexpected back-ground signal of NO₃ ( stray signal due to experimental set-up is also detected ) similar to laser induced fluorescence ( LIF ) excitation spectrum of the 0-0 band, although the back-ground signal was not expected in considering the 2C-R4WM scheme. Despite the back-ground interference, we have observed two peaks at 1051.61 and 1055.29 cm⁻¹ in the ν₁ region of the spectrum, and the frequencies agree with the two bands, 1051.2 and 1055.3 cm⁻¹, of our relatively higher resolution dispersed fluorescence spectrum, the former of which has been assigned to the ν₁ fundamental. Band width of both peaks,  ∼  0.2 cm⁻¹, is broader than twice the experimental spectral-resolution, 0.04 cm⁻¹ ( because this experiment is double resonance spectroscopy ), and the 1051.61 cm⁻¹ peak is attributed to a Q branch band head ( a line-like Q branch ) of the ν₁ fundamental. The other branches are suspected to be hidden in noise of the back-ground signal. The 1055.29 cm⁻¹ peak is also attributed to a Q band head. The B̃ ²E′_\frac12 ( J′ = \frac32, K′ = 1 ) - X̃ ²A₂′ ( N" = 1, K" = 0 ) ro-vibronic transition was used as the pump transition. The dump ( probe ) transition to both a₁′ and e′ vibronic levels are then allowed as perpendicular transition. Accordingly, it cannot be determined from present results whether the 1055.29 cm⁻¹ band is attributed to a₁′ or e′ (ν₃), unfortunately. The 2C-R4WM spectrum of the 1492 cm⁻¹ band region shows one Q head at 1499.79 cm⁻¹, which is consistent with our dispersed fluorescence spectrum. By considering with the ν₃ + ν₄ - ν₄ hot bandK. Kawaguchi et al., J. Phys. Chem. A 117, 13732 (2013) and E. Hirota, J. Mol. Spectrosco. 310, 99 (2015). the present results suggest that both 1055.29 and 1499.79 cm⁻¹ levels are a₁′ level.

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Footnotes:

K. Kawaguchi et al., J. Phys. Chem. A 117, 13732 (2013) and E. Hirota, J. Mol. Spectrosco. 310, 99 (2015).,

Rotationally-resolved high-resolution fluorescence excitation spectra of the ~B ²E′← ~X ²A₂′ electronic transition of ¹⁴NO₃ radical have been observed for 15860-15920 cm⁻¹ region. Sub-Doppler excitation spectra were measured by crossing a single-mode laser beam perpendicular to a collimated radical beam, which was formed by the heat decomposition of ¹⁴N₂O₅; ¹⁴N₂O₅ → ¹⁴NO₃ + ¹⁴NO₂. We have also measured the high-resolution fluorescence excitation spectra of the ¹⁴NO₂ Ã ²B₂ ← ~X ²A₁ transition to distinguish the ¹⁴NO₃ signals from the ¹⁴NO₂ signals in the observed region. The typical linewidth was 30 MHz and the absolute wavenumber was calibrated with accuracy 0.0001 cm⁻¹ by measurement of the Doppler-free saturation spectrum of iodine molecule and fringe pattern of the stabilized etalon. The observed rotational lines were too complicated to find any rotational series. In the observed spectra, only the rotational line pairs from the ~X ²A₂′(v"=0, K"=0, N"=1, F₁ and F₂) levels are assigned unambiguously by using the combination differences of the ~X ²A₂′ state and measurement of the Zeeman splittings similar to the analysis of the 0-0 band at around 15100 cm⁻¹ region. K. Tada, W. Kashihara, M. Baba, T. Ishiwata, E. Hirota, and S. Kasahara, J. Chem. Physc. 141, 184307 (2014).K. Tada, T. Ishiwata, E. Hirota, and S. Kasahara, J. Mol. Spectrosc., 321, 23 (2016). The observed results suggest the observed vibrationally excited states of the ~B ²E′ state are also interacts with the other vibronic levels similar to the ~B ²E′(v′=0) level. K. Tada, W. Kashihara, M. Baba, T. Ishiwata, E. Hirota, and S. Kasahara, J. Chem. Physc. 141, 184307 (2014).

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Footnotes:

The Jahn-Teller (JT) effect represents an enormous complication in the understanding of many molecules. We have been able to assign  ∼ 20 vibronic bands in the òE^′′ ← X̃²A₂′ transition of NO₃ and determine the linear and quadratic JT coupling terms for ν₃ and ν₄, indicating strong and weak JT coupling along these modes respectively. It was found that the experimental results quantitatively disagree with ones determined from a vibronic Hamiltonian based on high-level ab-initio theory.T. Codd, M.-W. Chen, M. Roudjane, J. F. Stanton, and T. A. Miller. Jet cooled cavity ringdown spectroscopy of the òE^′′ ← X̃²A′₂ Transition of the NO₃ Radical. J. Chem. Phys., 142:184305, 2015ypical analyses of experimental data use the quadratic JT Hamiltonian because limited measured levels tend to allow fitting only to coupling terms up to quadratic JT coupling. Hence, these analyses may neglect key contributions from cubic and quartic terms. To quantify this limitation, we have fit artificial spectra calculated with up to fourth order terms in the potential using a quadratic JT Hamiltonian and analyzed the results. The parameters chosen for this analysis are determined from ab-initio potentials for the à state of NO₃ and X̃ state of Li₃ to gain further insight on these molecules. Our initial results concerning the limitations of the quadratic JT Hamiltonian will be presented.

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Footnotes:

T. Codd, M.-W. Chen, M. Roudjane, J. F. Stanton, and T. A. Miller. Jet cooled cavity ringdown spectroscopy of the òE^′′ ← X̃²A′₂ Transition of the NO₃ Radical. J. Chem. Phys., 142:184305, 2015T

The magnitude of the Jahn-Teller (JT) effect in NO₃ has been the subject of considerable research in our group and other groups around the world. The rotational contour of the 4¹₀ vibronic band was first described by Hirota and coworkers using an oblate symmetric top.E. Hirota, T. Ishiwata, K. Kawaguchi, M. Fujitake, N. Ohashi, and I. Tanaka. Near-infrared band of the nitrate radical NO₃ observed by diode laser spectroscopy. J. Chem. Phys., 107:2829, 1997.eev et al. argued that an asymmetric top was required to describe the 2¹₀ band, although their spectrum was not completely rotationally resolved.A. Deev, J. Sommar, and M. Okumura. Cavity Ringdown Spectrum of the Forbidden òE^′′ ← X̃²A′₂ Transition of NO₃: Evidence for static Jahn-Teller Distortion in the à State. J. Chem. Phys., 122:224305, 2005.hese discrepancies suggest that a rotational analysis will provide considerable experimental information on the geometry of NO₃. Our group has collected high-resolution, rotationally resolved spectra of the vibronic òE^′′ ← X̃²A′₂ transitions. We have completed analysis of the 3¹₀ and 3¹₀4¹₀ parallel bands with a₁^′′ symmetry by using an oblate symmetric top with spin-rotation and centrifugal distortions. Several other parallel bands are now also reasonably understood. This analysis is consistent with a D_3\texth geometry for NO₃. In order to analyze the perpendicular bands with e′ symmetry, we have adapted the oblate symmetric top Hamiltonian from the previous analysis to include spin-orbit coupling, coriolis coupling, and Watson Terms (JT distortions) that allow the oblate symmetric top Hamiltonian to transition continuously to the distorted limit of C_2\textv symmetry. Preliminary analysis of the 2¹₀ and 2¹₀4²₀ bands has shown generally good agreement between model and experimental spectra. Our results indicate only modest JT distortions, although we do find evidence of multiple perturbations between these bands and high vibrational levels of the X̃ state. We will present our adapted Hamiltonian and the analysis of the 3¹₀, 3¹₀4¹₀, 2¹₀, and 2¹₀4²₀ bands.

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Footnotes:

E. Hirota, T. Ishiwata, K. Kawaguchi, M. Fujitake, N. Ohashi, and I. Tanaka. Near-infrared band of the nitrate radical NO₃ observed by diode laser spectroscopy. J. Chem. Phys., 107:2829, 1997.D A. Deev, J. Sommar, and M. Okumura. Cavity Ringdown Spectrum of the Forbidden òE^′′ ← X̃²A′₂ Transition of NO₃: Evidence for static Jahn-Teller Distortion in the à State. J. Chem. Phys., 122:224305, 2005.T

The ethynyl radical, C₂H, is a reactive intermediate important in various combustion processes and also widely observed in the interstellar medium. In spite of extensive previous spectroscopic studies, the characterization of the near infrared transitions from the ~X²Σ⁺ state to the mixed vibrational overtone and Ã²Π states is incomplete. A strong band of C₂H at 7064 cm⁻¹ was first observed in a neon matrix and assigned as the òΠ(002)¹ – ~X²Σ⁺ transition by Forney et al.D. Forney, M.E. Jacox, and W.E. Thompson, J. Mol. Spectrosc. 170, 178 (1995).ubsequent theoretical work of Tarroni and CarterR. Tarroni and S. Carter, Mol. Phys. 102, 2167 (2004).ttributed the strong absorptions in this region to transitions terminating in two upper states, each a mixture of vibrationally excited ~X states and different zero-order Ã-state bending levels: a ²Σ⁺ symmetry combination of ~X(0,2⁰,3) and Ã(0,3,0)⁰κ and a ²Π symmetry combination of ~X(0,3¹,3) and Ã(0,0,2)¹. Transitions to them from the zero point level of the ~X state are calculated to differ in energy by less than 10 cm⁻¹ and to be within a factor of two in intensity. Diode laser transient absorption was used to record Doppler-limited spectra between 7020 and 7130 cm⁻¹, using 193 nm photolysis of CF₃C₂H as a source of C₂H. Two interleaved, rotationally resolved bands were observed, consistent with a ²Σ - ²Σ transition at 7088 cm⁻¹ and a ²Π - ²Σ transition at 7108 cm⁻¹, in good accord with the Tarroni and Carter calculation. Progress on the assignment and fitting of the spectra will be reported. Acknowledgements: Work at Brookhaven National Laboratory was carried out under Contract No. DE-SC0012704 with the U.S. Department of Energy, Office of Science, and supported by its Division of Chemical Sciences, Geosciences, and Biosciences.

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D. Forney, M.E. Jacox, and W.E. Thompson, J. Mol. Spectrosc. 170, 178 (1995).S R. Tarroni and S. Carter, Mol. Phys. 102, 2167 (2004).a

Recently, we carried out the perturbation analysis of C₂ spectra and identified forbidden singlet-triplet intersystem transitions,W. Chen, K. Kawaguchi, P. F. Bernath, and J. Tang, J. Chem. Phys., 142, 064317 (2015).hich aroused further interest in other C₂ spectra for the many low-lying electronic states of this fundamental molecule. In 1988, the B¹∆_g-A¹Π_u and B′¹Σ_g⁺-A¹Π_u band systems were discovered by Douay et al.,M. Douay, R. Nietmann and P. F. Bernath, J. Mol. Spectrosc., 131, 261 (1988).ho observed eight bands of the B¹∆_g-A¹Π_u system with v up to 5 for the B¹∆_g state and six bands of the B′¹Σ_g⁺-A¹Π_u system with v up to 3 for the B′¹Σ_g⁺ state in the Fourier transform infrared emission spectra of hydrocarbon discharges. In the work presented here, we identified twenty-four bands of the two systems, among which the B′¹Σ_g⁺ v = 4 and the B¹∆_g v = 6, 7 and 8 vibrational levels involved in nine bands were studied for the first time. A direct global analysis with Dunham parameters was carried out satisfactorily for the B¹∆_g-A¹Π_u system except for a small perturbation in the B¹∆_g v = 6 level. The calculated rovibrational term energies up to B¹∆_g v = 12 showed that the level crossing between the B¹∆_g and d³Π_g states is responsible for many of the prominent perturbations in the Swan system observed previously.A. Tanabashi, T. Hirao, T. Amano and P. F. Bernath, Astrophys. J. Suppl. Ser., 169, 472 (2007).ineteen lines of the B¹∆_g-a³Π_u forbidden transitions were identified and the off-diagonal spin-orbit interaction constant A_dB between d³Π_g and B¹∆_g was derived as 8.3(1) cm⁻¹. For the B′¹Σ_g⁺-A¹Π_u system, only individual band analyses for each vibrational level in the B′¹Σ_g⁺ state could be done satisfactorily and Dunham parameters obtained from these effective parameters showed that the anharmonic vibrational constant ω_e x_e is anomalously small (nearly zero). Inspection of the RKR potential curves for the B′¹Σ_g⁺ and X¹Σ_g⁺ states revealed that an avoided crossing may occur around 30000 cm⁻¹, which is responsible for the anomalous molecular constants in these two states.W. Chen, K. Kawaguchi, P. F. Bernath, and J. Tang, J. Chem. Phys., 144, 064301 (2016).html:<hr /><h3>Footnotes: W. Chen, K. Kawaguchi, P. F. Bernath, and J. Tang, J. Chem. Phys., 142, 064317 (2015).w M. Douay, R. Nietmann and P. F. Bernath, J. Mol. Spectrosc., 131, 261 (1988).w A. Tanabashi, T. Hirao, T. Amano and P. F. Bernath, Astrophys. J. Suppl. Ser., 169, 472 (2007).N W. Chen, K. Kawaguchi, P. F. Bernath, and J. Tang, J. Chem. Phys., 144, 064301 (2016).

The ground X̃²E vibrations of the methoxy radical have intrigued both experimentalists and theorists alike due to the presence of a conical intersection at the C_3v molecular geometry. This conical intersection causes methoxy's vibrational spectrum to be strongly influenced by Jahn-Teller vibronic coupling which leads to large amplitude vibrations and extensive mixing of the two lowest electronic states. This coupling combined with spin-orbit and Fermi couplings greatly complicates the assignments of states.
Using the potential force field and calculated spectra of Nagesh and Sibert^1,2, we assign quantum numbers to the infrared spectrum. When the zero-order states are the diabatic normal mode states, there is sufficient mode mixing that the normal mode quantum numbers are poor labels for the final states. We define a series of zero-order Hamiltonians which include additional coupling elements beyond the normal mode picture but still allow for the assignment of Jahn-Teller quantum numbers. In methoxy, the two lowest frequency e modes, the bend (q₅) and the rock (q₆), are the modes with the strongest Jahn-Teller coupling. In general, a zero-order Hamiltonian which includes first-order Jahn-Teller coupling in q₆ is sufficient for most states of interest. Working in a representation which includes first-order Jahn-Teller coupling in q₆, we identify states in which additional coupling elements must be included; these couplings include first-order Jahn-Teller coupling in q₅, higher order Jahn-Teller coupling in q₅ and q₆, and, in the dueterated case, Jahn-Teller coupling which is modulated by the corresponding a modes.

¹

Nagesh, J.; Sibert, E. L. J. Phys. Chem. A 2012, 116, 3846-3855.

²

Lee, Y.F.; Chou, W.T.; Johnson, B.A.; Tabor, D.P. ; Sibert, E.L.; Lee, Y.P. J. Mol. Spectrosc. 2015, 310, 57-67.

²

Barckholtz, T. A.; Miller, T. A. Int. Revs. in Phys. Chem. 1998, 17, 435-524.

The Criegee intermediates are carbonyl oxides that play critical roles in ozonolysis of alkenes in the atmosphere. We reported previously the mid-infrared spectra of the simplest Criegee intermediate CH₂OO. Y.-T.  Su, Y.-H.  Huang, H. A.  Witek, Y.-P.  Lee, Science 340, 174 (2013).^, Y.−H.  Huang, J.  Li, H.  Guo, Y.−P.  Lee, J. Chem. Phys. 142, 214301 (2015).nd the methyl−substituted intermediate CH₃CHOO. H.−Y.  Lin, Y.−H.  Huang, X.  Wang, J. M.  Bowman, Y.  Nishimura, H. A.  Witek, Y.−P.  Lee, Nat. Comm. 6, 7012 (2015).ere we report the transient infrared spectrum of (CH₃)₂COO, produced on UV photolysis of a mixture of (CH₃)₂CI₂, N₂, and O₂ in a flow reactor, using a step−scan Fourier−transform spectrometer. Guided by results of quantum−chemical calculations, rotational contours of the four observed bands are simulated successfully and provide definitive identification of (CH₃)₂COO. Although all observed bands of (CH₃)₂COO contain hot bands from four vibrational modes of low energy, we were able to simulate the spectra satisfactorily. Observed bands with origins near 887, 1040, 1368, and 1422 cm^-1 agree satisfactorily with corresponding anharmonic vibrational wavenumbers at 903, 1061, 1364, and 1422 cm^-1 Y.-H. Huang, J. Li, H. Guo, Y.-P. Lee, J. Chem. Phys. 142, 214301 (2015).a H.-Y. Lin, Y.-H. Huang, X. Wang, J. M. Bowman, Y. Nishimura, H. A. Witek, Y.-P. Lee, Nat. Comm. 6, 7012 (2015).H

Cavity ringdown, near-infrared spectra have been previously observed following the photolysis of the dihalomethanes(CH₂XI, X = I, Br, Cl) in the presence of O₂ and N₂. In last year's SymposiumN. D. Kline, M. Huang, T. A. Miller, P. Lolur, R. Dawes, FD05, 70th International Symposium of Molecular Spectroscopy(2015) we presented evidence that all the spectra could be attributed to the Ã-~X electronic transition of the appropriate CH₂XOO· radical. We now present detailed analyses of these spectra. Similar spectral features have been observed for all radicals. The first strong transitions are located around 6800 cm⁻¹, and are assigned as associated with the origin. Other strong transitions are observed about 800 cm⁻¹ blue of the origin, and have a multiple-peak structure similar to the corresponding origin bands. These bands are assigned to be the OO stretch of the Ã-~X electronic transitions, which are typically strong in the spectra of peroxy radicals, based on electronic structure calculations that provide vibrational frequencies and Franck-Condon factors. One-dimensional calculations of the internal torsion mode are applied to specifically explain the multiple-peak features in both the origin and OO stretch region as series of transitions including sequence bands and other hot bands from the vibrationally excited states of the low-frequency torsion mode in the ~X state, which are significantly populated at room temperature. Additional bands can be assigned to fundamentals or combination bands of various other à state modes.

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Footnotes:

N. D. Kline, M. Huang, T. A. Miller, P. Lolur, R. Dawes, FD05, 70th International Symposium of Molecular Spectroscopy(2015),

r0pt Figure NO₂, a toxic gas formed in most combustion processes, plays an important role in the Earth's atmosphere due to its role in the production of both photochemical smog and tropospheric ozone. The existence of the peroxy radial, NOO, has been proposed, both as a collision reaction intermediate, and as a negative-ion in some discharge sources, in order to account for extended tails seen in some photoelectron spectra.K. M. Ervin and J. Ho and W. C. Lineberger, J. Phys. Chem. 92, 5405 (1988). doi:10.1021/j100330a017n this work a velocity-mapped image of NO₂⁻ photodetachment measured at 519 nm, shown, reveals high-energy electron structure, that persists at detachment energies lower than the electron affinity of ONO, 2.273 eV. The central ring has the spectral signature of O⁻, while the outer-ripples, that appear in character to be similar to NO− detachment, are, we propose due to the NOO⁻ peroxy radical, which is also responsible for the presence of O⁻. The photoelectron spectrum resolves the vibrational structure to characterize the neutral peroxy radical. The identification is further supported by ab initio calculations. The photoelectron angular distributions associated with the peroxy radical have a negative anisotropy parameter, opposite in sign to detachment from ONO⁻.

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K. M. Ervin and J. Ho and W. C. Lineberger, J. Phys. Chem. 92, 5405 (1988). doi:10.1021/j100330a017I

The n-propyl and i-propyl radicals were generated in the gas phase via pyrolysis of n-butyl nitrite (CH₃(CH₂)₃ONO) and i-butyl nitrite (CH₃CH(CH₃)CH₂ONO) precursors, respectively. Nascent radicals were promptly solvated by a beam of He nanodroplets, and the infrared spectra of the radicals were recorded in the C-H stretching region. In addition to three vibrations of n-propyl previously measured in an Ar matrix, we observe many unreported bands between 2800 and 3150 cm⁻¹, which we attribute to propyl radicals. The C-H stretching modes observed above 2960 cm⁻¹for both radicals are in excellent agreement with anharmonic frequencies computed using VPT2. Between 2800 and 2960 cm⁻¹, however, the spectra of n-propyl and i-propyl radicals become quite congested and difficult to assign due to the presence of multiple anharmonic resonances. Computations employing a local mode Hamiltonian reveal the origin of the spectral congestion to be strong coupling between the high frequency C-H stretching modes and the lower frequency bending/scissoring motions. The only significant local coupling is between stretches and bends on the same CH₂/CH₃ group.

Fulvenallene (C₇H₆) and the fulvenallenyl (C₇H₅) radical are produced via thermal dissociation of phthalide in a continuous-wave SiC pyrolysis furnace. Prompt pick-up and solvation by helium droplets allows for well-resolved vibrational spectra of these species in the CH stretching region. The acetylenic CH stretch of the fulvenallenyl radical is a sensitive marker of the extent by which the unpaired electron is delocalized throughout the conjugated propargyl and cyclopentadienyl subunits. The nature of this electron delocalization is explored with spin density calculations at the CCSD(T)/ANO1 level of theory.

Pyrolytic dissociation of Cl₂ is employed to dope helium droplets with single Cl atoms. Sequential addition of NH₃ to Cl-doped droplets leads to the formation of a complex residing in the entry valley to the substitution reaction, Cl + NH₃ → ClNH₂ + H. Infrared Stark spectroscopy in the NH stretching region reveals symmetric and antisymmetric vibrations of a C_3v symmetric top. Frequency shifts from NH₃ and dipole moment measurements are consistent with a ClNH₃ complex containing a relatively strong two-center three-electron (2c-3e) bond. The nature of the 2c-3e bonding in ClNH₃ is explored computationally and found to be consistent with the complexation-induced blue shifts observed experimentally. Computations of interconversion pathways reveal nearly barrierless routes to the formation of this complex, consistent with the absence of two other complexes, NH₃Cl and Cl-HNH₂, which are predicted in the entry valley to the hydrogen abstraction reaction, Cl + NH₃ → HCl + NH₂

Whereas the benzyl radical, a prototypic aromatic free radical, has been the subject of numerous spectroscopic studies, halo-substituted benzyl radicals have received less attention, due to the difficulties associated with production of radicals from precursors. In particular, chloro-substituted benzyl radicals have been much less studied because of the weak visible emission intensity and weak C-Cl bond dissociation energy. The jet-cooled chlorofluorobenzyl radicals were generated in a technique of corona excited supersonic jet expansion using a pinhole-type glass nozzle for the vibronic assignments and measurements of electronic energies of the D₁ → D₀ transition. The 2,4-,C. S. Huh, Y. W. Yoon, and S. K. Lee, J. Chem. Phys. 136, 174306 (2012).,5-,Y. W. Huh, S. Y. Chae, and S. K. Lee, Chem. Phys. Lett. 608, 6 (2014).nd 2,6- Y. W. Yoon, S. Y. Chae, M. Lim, and S. K. Lee, Chem. Phys. Lett. 637, 148 (2015).hlorofluorobenzyl radicals were generated by corona discharge of corresponding precursors, chlorofluorotoluenes seeded in a large amount of helium carrier gas. The vibronic emission spectra were recorded with a long-path monochromator in the visible region. The emission spectra show the vibronic bands originating from two types of benzyl-type radicals, chlorofluorobenzyl and fluorobenzyl benzyl radicals, in which fluorobenzyl radicals were obtained by displacement of Cl by H produced by dissociation of methyl C-H bond. From the analysis of the spectra observed, we could determine the electronic energies in D₁ → D₀ transition and vibrational mode frequencies at the D₀ state of chlorofluorobenzyl radicals, which show the origin band of the electronic transition to be shifted to red region, comparing with the parental benzyl radical. From the quantitative analysis of the red-shift, it has been found that the additivity rule can be applied to dihalo-substituted benzyl radicals. In this presentation, the dissociation process of precursors in corona discharge is discussed in terms of bond dissociation energy as well as the spectroscopic analysis of the radicals.

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Footnotes:

C. S. Huh, Y. W. Yoon, and S. K. Lee, J. Chem. Phys. 136, 174306 (2012).2 Y. W. Huh, S. Y. Chae, and S. K. Lee, Chem. Phys. Lett. 608, 6 (2014).a Y. W. Yoon, S. Y. Chae, M. Lim, and S. K. Lee, Chem. Phys. Lett. 637, 148 (2015).c

Combustion of organosulfur contaminants in petroleum-based fuels and biofuels produces sulfur oxides (SO_x). These pollutants are highly regulated by the EPA because they have been linked to poor respiratory health and negative environmental impacts. Therefore much effort has been made to remove sulfur compounds in petroleum-based fuels and biofuels. Currently desulfurization methods used in the fuel industry are costly and inefficient. Research of the thermal decomposition mechanisms of organosulfur species can be implemented via engineering simulations to modify existing refining technologies to design more efficient sulfur removal processes. We have used a resistively-heated SiC tubular reactor to study the thermal decomposition of ethanethiol (CH₃CH₂SH) and dimethylsulfide (CH₃SCH₃). The decomposition products are identified by two independent techniques: 118.2 nm VUV photoionization mass spectroscopy and infrared spectroscopy. The thermal cracking products for CH₃CH₂SH are CH₂CH₂, SH, and H₂S and the thermal cracking products from CH₃SCH₃ are CH₃S, CH₂S, and CH₃.