We demonstrate the potential of THz spectroscopy to monitor the real time evolution of the gas phase concentration of photolysis products and determine the kinetic reaction rate constantH. M. Pickett and T. L. Boyd, Chem. Phys. Lett, Vol 58, 446-449, (1978) In the primary work, we have chosen to examine the photolysis of formaldehyde (H₂CO) S. Eliet, A. Cuisset, M Guinet, F. Hindle, G. Mouret, R. Bocquet, and J. Demaison, Journal of Molecular Spectroscopy, Vol 279, 12-15 (2012). Exposure of H₂CO to a UVB light (250 to 360 nm) in a single pass of 135 cm length cell leads to decomposition via two mechanisms: the radical channel with production of HCO and the molecular channel with production of CO. A commercial THz source G. Mouret, M. Guinet, A. Cuisset, L. Croizé, S. Eliet, R. Bocquet and F. Hindle, Sensors Journal. IEEE, Vol 13, 133 – 138, (2013)frequency multiplication chain) operating in the range 600-900 GHz was used to detect and quantify the various chemical species as a function of time. Monitoring the concentrations of CO and H₂CO via rotational transitions, allowed the kinetic rate of H₂CO consummation to be obtained, and an estimation of the rate constants for both the molecular and radical photolysis mechanisms. We have modified our experimental setup to increase the sensitivity of the spectrometer and changed sample preparation protocol specifically to quantify the HCO concentration. Acetaldehyde was used as the precursor for photolysis by UVC resulting in the decompositon mechanism can be described by:

CH3CHO+hν→ CH3 + HCO → CH4 + CO

Frequency modulation of the source and Zeeman modulation is used to achieve the high sensitivity required. Particular attention has been paid to the mercury photosensitization effect that allowed us to increase the HCO production enabling quantification of the monitored radical. We quantify the HCO radical and start a spectroscopic study of the line positions.

---

Footnotes:

H. M. Pickett and T. L. Boyd, Chem. Phys. Lett, Vol 58, 446-449, (1978) . S. Eliet, A. Cuisset, M Guinet, F. Hindle, G. Mouret, R. Bocquet, and J. Demaison, Journal of Molecular Spectroscopy, Vol 279, 12-15 (2012). . G. Mouret, M. Guinet, A. Cuisset, L. Croizé, S. Eliet, R. Bocquet and F. Hindle, Sensors Journal. IEEE, Vol 13, 133 – 138, (2013)(

It is well known that as molecules become larger the spectral lines of their high-resolution rotational spectra begin to merge, first into modest blends, then into clusters of many lines, and finally into continua. In addition to impacting specificity, the usual signal processing strategies used to separate spectral information from background become ineffective. Medium Resolution Cavity Spectroscopy trades the usual excess of specificity of rotational spectroscopy for a means of obtaining spectra of large molecules with congested or semi-continua spectra. The chief scientific question to be answered is how large (according the several definitions of ‘large’) can a molecule be and still have structure at medium resolution. The chief technical question to be answered is how to develop strategies to approach white noise sensitivity limits. Experimental details and results, and theoretical results will be presented.

Submillimeter/Infrared Double Resonance is a well-established technique. It has been used for spectroscopy, studies of collisional energy transfer, and diagnostics. The high level of molecule specific spectroscopic specificity achieved through this technique makes it an attractive candidate for sensor application. Here we will discuss its application to sensor development, with emphasis on regimes of applicability that range from mTorr to atmospheric pressure. System requirements and development as well as theoretical and experimental results will be discussed.

Rotational and rovibrational spectra of methyl cyanide were recorded to analyze interactions in low-lying vibrational states and to construct line lists for radio astronomical observations as well as for infrared spectroscopic investigations of planetary atmospheres. The rotational spectra cover large portions of the 36−1627 GHz region.Part of this work was carried out at the Jet Propulsion Laboratory under contract with the National Aeronautics and Space Administration.n the infrared (IR), a spectrum was recorded for this study in the region of 2ν₈ around 717 cm⁻¹ with assignments covering 684−765 cm⁻¹. Additional spectra in the ν₈ region were used to validate the analysis. Using ν₈ dataM. Koivusaari et al., J. Mol. Spectrosc. 152 (1992) 377−388.s well as spectroscopic parameters for v₄ = 1, v₇ = 1, and v₈ = 3 from previous studies,A.-M. Tolonen et al., J. Mol. Spectrosc. 160 (1993) 554−565.e analyzed rotational data involving v = 0, v₈ = 1, and v₈ = 2 up to high J and K quantum numbers. We analyzed a strong ∆v₈ = ±1, ∆K = 0, ∆l = ±3 Fermi resonance between v₈ = 1⁻¹ and v₈ = 2⁺² at K = 14 and obtained preliminary results for two further Fermi resonances between v₈ = 2 and 3. We also found resonant ∆v₈ = ±1, ∆K = ±2, ∆l = ±1 interactions between v₈ = 1 and 2 and present the first detailed analysis of such a resonance between v₈ = 0 and 1. We discuss the impact of this analysis on the v₈ = 1 and 2 as well as on the axial v = 0 parameters and compare selected CH₃CN parameters with those of CH₃CCH and CH₃NC. We evaluated transition dipole moments of ν₈, 2ν₈ − ν₈, and 2ν₈ for remote sensing in the IR.

---

Footnotes:

Part of this work was carried out at the Jet Propulsion Laboratory under contract with the National Aeronautics and Space Administration.I M. Koivusaari et al., J. Mol. Spectrosc. 152 (1992) 377−388.a A.-M. Tolonen et al., J. Mol. Spectrosc. 160 (1993) 554−565.w

Understand the molecular dynamics on buried electrodes under electrochemical transformations is of significant interest. There is a big gap of knowledge in the CO₂ electroreduction mechanism due to the limitations to access and probe the liquid-metal interfaces [1,2]. Vibrational Sum Frequency Spectroscopy (VSFS) is a non-invasive and surface sensitive technique, with molecular level detection that can be used to probe electrochemical reactions occurring on the electrolyte-electrode interface [2]. We observed the CO₂ electroreduction to CO in ionic liquids (ILs) on poly Ag using VSFS synchronized with cyclic voltammetry. In order to follow the CO₂ reaction in situ on the ionic liquid-Ag interface; the CO, CO₂ and imidazolium vibrational modes (resonant SFS) were monitored as a function of potential. We identified at which potential the CO was produced and how the EMIM-BF₄ played an important role in the electron transfer to the CO₂, lowering the CO₂⁻ energy barrier. A new approach to reveal the double layer dynamics to the electrostatic environment is presented by the study of the nonresonant sum frequency intensity as a function of the applied potential. By this method, we studied the influence of water-ionic liquid mixtures in the CO₂ electroreduction on Ag electrode. We observed a shift to lower potentials in the CO₂ electroreduction in water-ILs electrolyte. Previous studies in gas diffusion fuel cells have shown the CO₂ electroreduction in a water-imidazolium–based ILs on Ag nanoparticles at lower overpotential [3]. Our VSFS study helps to understand the fundamental electrochemical mechanism, showing how the ILs structural transition influences the CO₂ electroreduction. [1] Polyansky, D. E.; Electroreduction of Carbon Dioxide, 2014, Encyclopedia of Applied Electrochemistry, Springer New York, pag 431-437. [2] Bain, C. D.; J. Chem. Soc., Faraday Trans., 1995, 91, 1281. [3] Rosen, B. A. et al; Science, 2011, 334 (6056), 643. Rosen, B. A. et al.; J. electrochem. Soc., 2013, 160 (2), H138.

The technique Noise Immune Cavity Enhanced Optical Heterodyne Velocity Modulation Spectroscopy, or NICE-OHVMS, has been used to great effect to precisely and accurately measure a variety of molecular ion transitions from species such as H₃⁺, CH₅⁺, HeH⁺, and HCO⁺, achieving MHz or in some cases sub-MHz uncertainty.J. N. Hodges, et al. J. Chem. Phys. (2013), 139, 164201.A. J. Perry, et al. J. Chem. Phys. (2014), 141, 101101. It is a powerful technique, but a complete theoretical understanding of the complex NICE-OHVMS lineshape is needed to fully unlock its potential.
NICE-OHVMS is the direct result of the combination of the highly sensitive spectroscopic technique Noise Immune Cavity Enhanced Optical Heterodyne Molecular Spectroscopy(NICE-OHMS) with Velocity Modulation Spectroscopy(VMS), applying the most sensitive optical detection method with ion species selectivity.K. N. Crabtree, et al. Chem. Phys. Lett. (2012), 551, 1-6.he theoretical underpinnings of NICE-OHMS lineshapes are well established,F. M. Schmidt, et al. J. Opt. Soc. Amer. A (2008), 24, 1392-1405.s are those of VMS.J. W. Farley, J. Chem. Phys. (1991), 95, 5590-5602.his presentation is the logical extension of those two preceding bodies of work. Simulations of NICE-OHVMS lineshapes under a variety of conditions and fits of experimental data to the model are presented. The significance and accuracy of the various inferred parameters, along with the prospect of using them to extract additional information from observed transitions, are discussed.

---

Footnotes:

J. N. Hodges, et al. J. Chem. Phys. (2013), 139, 164201.

---

Footnotes:

K. N. Crabtree, et al. Chem. Phys. Lett. (2012), 551, 1-6.T F. M. Schmidt, et al. J. Opt. Soc. Amer. A (2008), 24, 1392-1405.a J. W. Farley, J. Chem. Phys. (1991), 95, 5590-5602.T

Plasmas at atmospheric pressure serve many purposes, from ionization sources for ambient mass spectrometry (AMS) to plasma-assisted wound healing. Of the many naturally occurring ambient plasmas, ball lightning is one of the least understood; there is currently no solid explanation in the literature for the formation and lifetime of natural ball lightning. With the first measurements of naturally occurring ball lightning being reported last year,Cen, J.; Yuan, P,; Xue, S. Phys. Rev. Lett. 2014, 112, 035001.e have worked to replicate the natural phenomenon in order to elucidate the physical and chemical processes by which the plasma is sustained at ambient conditions. We are able to generate ball-shaped plasmoids (self-sustaining plasmas) that are analogous to natural ball lightning using a high-voltage, high-current, pulsed DC system.Dubowsky, S.E.; Friday, D.M.; Peters, K.C.; Zhao, Z.; Perry, R.H.; McCall, B.J. Int. J. Mass Spectrom. 2015, 376, 39-45.mprovements to the discharge electronics used in our laboratory and characterization of the plasmoids that are generated from this system will be described. Infrared emission spectroscopy of these plasmoids reveals emission from water and hydroxyl radical - fitting methods for these molecular species in the complex experimental spectra will be presented. Rotational temperatures for the stretching and bending modes of H₂O along with that of OH will be presented, and the non-equilibrium nature of the plasmoid will be discussed in this context.

---

Footnotes:

Cen, J.; Yuan, P,; Xue, S. Phys. Rev. Lett. 2014, 112, 035001.w Dubowsky, S.E.; Friday, D.M.; Peters, K.C.; Zhao, Z.; Perry, R.H.; McCall, B.J. Int. J. Mass Spectrom. 2015, 376, 39-45.I

A quantified description of photoemission from thruster plume species, such as water and ammonia, is necessary for complete characterization of a thruster plume. Photoemission in a plume is due to excitation of molecular species from solar photons. For instance, electronic excitation of water with Lyman-alpha (121.6 nm) causes dissociation to the OH radical by following one of several possible pathways. One pathway leads to an electronically excited OH radical which fluoresces near 300 nm. Here, four-wave mixing is used to generate vacuum ultraviolet photons to excite a plume species seeded in a jet expansion. The resulting fluorescence is analyzed and used to describe the temperature dependence of the fluorescence signature.

The pyrolysis of 3-oxetanone, O(CH₂)₂CO, has been studied in a resistively heated SiC tubular reactor at 400-1200 ^°C. Products of pyrolysis were identified via matrix-isolation FTIR spectroscopy and photoionization mass spectrometry in separate experiments. While 3-oxetanone is expected to dissociate into ketene and formaldehyde, these experiments show that ethylene oxide and carbon monoxide are also produced. Methyl radical and ethylene were observed as additional products and are thought to be the result of reactions involving ethylene oxide.

In this work, we could experimentally achieved the generation of white-light laser pulses of few-cycle fs pulses using a neon-filled hollow-core fiber. The observed pulses reached 6-fs at at repetition rate of 1 kHz using 2.5 mJ of 31 fs femtosecond pulses. The pulse compressing achieved by the supercontinuum produced in static neon-filled hollow fibers while the dispersion compensation is achieved by five pairs of chirped mirrors. We showed that gas pressure can be used to continuously vary the bandwidth from 350 nm to 900 nm. Furthermore, the applied technique allows for a straightforward tuning of the pulse duration via the gas pressure whilst maintaining near-transform-limited pulses with constant output energy, thereby reducing the complications introduced by chirped pulses. Through measurements of the transmission through the fiber as a function of gas pressure, a high throughput exceeding 60% was achieved. Adaptive pulse compression is achieved by using the spectral phase obtained from a spectral phase interferometry for direct electric field reconstruction (SPIDER) measurement as feedback for a liquid crystal spatial light modulator (SLM). The spectral phase of these supercontinua is found to be extremely stable over several hours. This allowed us to demonstrate successful compression to pulses as short as 5.2 fs with controlled wide spectral bandwidth, which could be used to excite different states in complicated molecules at once.