A SLIT-JET INFRARED SPECTRUM OF 1,3-BUTADIENE

Author Institution: JILA. University of ColoradoA slit-jet infrared spectrum of the CH stretching fundamental band $\nu_{1}$ of trans-1,3-butadiene has been measured with a difference frequency laser system in the wavenumber region $3090 - 3120 cm^{-1}$. The optical resolution of the spectrum is about 100 MHz. An $a/b$-type hybrid band structure is observed. A detailed analysis, of spectrum will be presented, and the role of large amplitude motion and intramolecular vibrational energy redistribution will be discussed

BRIDGING THE GAP BETWEEN VAN DER WAALS AND HYDROGEN BONDING: A NEAR-IR STUDY OF THE INTERMOLECULAR MODES IN HCl DIMER

Author Institution: JILA, National Institute of Standards and Technology and Department of Chemistry and Biochemistry, University of ColoradoThe near IR combination band spectra of supersonically cooled $(HCL)_{2}$ in the $2900 cm^{-1}$ to $3070 cm^{-1}$ region have been recorded with a high resolution slit jet spectrometer. Seven vibration-rotation-tunneling (VRT) bands are observed, representing 3 (out of 4 total) intermolecular modes (van der Waals stretch $v_{4}$, geared bend $v_{5}$, and out-of-plane torsion $v_{6}$) built as combination bands on either the $v_{1}$ (free) or $v_{2}$ (bound) HCl stretches. Each of the seven combination bands are observed for both the $H^{35}Cl-H^{35}Cl$ and $H^{35}Cl-H^{37}Cl$ isotopomers. Analysis of the rotationally resolved spectra provide spectroscopic constants, intermolecular frequencies, predissociation rates, and isotopic shifts as a function of both intra- and inter-molecular excitation. The intermolecular frequencies are compared with full 6-D quantum calculations of a trial potential surface and discrepencies are discussed. Additionally, comparisons with similar studies on $(HF)_{2}$ and $(DF)_{2}$ are presented. Both tunneling rates and combination band intensities are compared between the chlorine and fluorine build dimers, illuminating dramatic differences in these seemingly similar hydrogen bonded prototypes

VELOCITY MODULATION SPECTROSCOPY OF MOLECULAR IONS IN A SUPERSONIC SLIT JET DISCHARGE

Author Institution: JILA, National Institute of Standards and Technology and Department of Chemistry and Biochemistry, University of ColoradoWe report an experimental apparatus for velocity modulation spectroscopy of molecular ions in a supersonic slit jet discharge. Rotationally and translationally (T | 25 K) molecular ions are generated in a glow discharge, slit supersonic expansion. Detection of the ions is achieved via direct absorption of a high resolution (| 2 MHz) near infrared laser. Electrodes aligned perpendicular to the slit expansion provide a modulating electric field (300-500 V/cm at 30-100 KHz) which in turn modulates the absorption via Doppler shifts of the molecular ions. Lock-in detection at the modulation frequency provides descrimination both from low frequency noise and neutral species absorption. The sensitivities achieved and possible limitations will be discussed. Additionally, the most recent results obtained with this apparatus will be presented

Driving photochemistry by clustering: The ICl-Xe case

We present slice imaging data demonstrating the influence of clustering on the photodissociation dynamics of a diatomic molecule: iodine monochloride (ICl) was dissociated at 235 nm in He and Xe seed gasses, probing both Cl and I photofragment energy and angular distributions. We observe that the kinetic energy releases of both Cl and I fragments change from He to Xe seeding. For Cl fragments, the seeding in Xe increases the kinetic energy release of some Cl fragments with a narrow kinetic energy distribution, and leads to some fragments with rather broad statistical distribution falling off exponentially from near-zero energies up to about 2.5 eV. Iodine fragment distribution changes even more dramatically from He to Xe seeding: sharp features essentially disappear and a broad distribution arises reaching to about 2.5 eV. Both these observations are rationalized by a simple qualitative cluster model assuming ICl dissociation inside larger xenon clusters and on surface of smaller Xe species. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4758317

JET COOLED LASER SPECTROSCOPY OF HYDROCARBON RADICALS AND MOLECULAR IONS IN SLIT SUPERSONIC EXPANSIONS

Author Institution: JILA National Institute for Standards and Technology, Department of Chemistry and Biochemistry, University of ColoradoThe novel combination of pulsed slit supersonic expansions and pulsed electrical discharges results in a remarkably intense source of jet cooled chemical reactive species in a long path length geometry ideal for near shot noise limited direct absorption spectroscopy with high resolution tunable lasers. This proves particulary powerful in the near infrared, where the reduced Doppler linewidths in the slit jet permits rovibrational, open shell fine structure and sometimes even hyperfine structure to be resolved. Most importantly this method provides access to spectra of transient species at very low temperatures (10K), which greatly simplifies the resulting spectroscopic assignment and analysis. This talk will develop the background methodology of these slit discharge methods and then discuss three sample hydrocarbon radical systems studied: from 1) the relatively simple methyl ($CH_{3}$) radical, which by virtue of sub-Doppler linewidths permits both Fermi contact information on gas phase spin densities to be extracted for the first time and elucidates the effects of spin polarization through CH molecular bonds, 2) the more complicated ethyl ($CH_{3}CH_{2}$) radical, which exhibits strongly coupled large amplitude motion between wagging of the $CH_{2}$ radical center and internal rotation around the C-C bond, to 3) the allyl ($CH_{2}CHCH_{2}$)radical, which represents the fundamental paradigm for electron delocalization in a $\pi$ system. Time permitting, recent extensions to high frequency discharge modulation techniques and applications to jet cooled molecular ion spectroscopy will also be discussed

Newton-Okounkov bodies sprouting on the valuative tree

Agraïments: This research was started during the workshop "Recent advances in Linear series and Newton-Okounkov bodies", which took place in Padova, Italy, February 9-14, 2015. The authors enjoyed the lively and stimulating atmosphere of that event. Michal Farnik was partially supported by the Polish National Science Centre, grant number 2015/17/B/ST1/02637. Constantin Shramov was partially supported by the Russian Academic Excellence Project 5-100', by RFBR grants 15-01-02164, 15-01-02158, 14-01-00160, and by Dynasty foundation.Given a smooth projective algebraic surface X, a point O∈X and a big divisor D on X, we consider the set of all Newton-Okounkov bodies of D with respect to valuations of the field of rational functions of X centred at O, or, equivalently, with respect to a flag (E, p) which is infinitely nearO, in the sense that there is a sequence of blowups X'→X, mapping the smooth, irreducible rational curve E⊂X' to O. The main objective of this paper is to start a systematic study of the variation of these infinitesimal Newton-Okounkov bodies as (E, p) varies, focusing on the case X=P2

Runaway electron diagnostics for the COMPASS tokamak using EC emission

An electron cyclotron emission (ECE) diagnostic of suprathermal electrons was utilised for runaway electron (RE) experiments purposes in the COMPASS tokamak. Our vertical ECE (V-ECE) system consists of a 16-channel heterodyne radiometer and an E-band horn antenna with a 76.5-88 GHz frequency range front-end. Simulations used for the design of the diagnostic showed a possibility of detecting the emission of low-energy (50-140 keV) runaway electrons. We realized measurements with both extraordinary (X-) and ordinary (O-) mode linear polarizations. The amplitudes of the X-mode and O-mode signals are similar, which can be explained by depolarised reflected radiation. V-ECE measurements in low-density flattop discharges and in discharges with massive gas injections of high-Z elements show correlations with other RE diagnostics. Our results are in the agreement with the principles of the primary runaway generation mechanisms

Runaway electron diagnostics for the COMPASS tokamak using EC emission

An electron cyclotron emission (ECE) diagnostic of suprathermal electrons was utilised for runaway electron (RE) experiments purposes in the COMPASS tokamak. Our vertical ECE (V-ECE) system consists of a 16-channel heterodyne radiometer and an E-band horn antenna with a 76.5-88 GHz frequency range front-end. Simulations used for the design of the diagnostic showed a possibility of detecting the emission of low-energy (50-140 keV) runaway electrons. We realized measurements with both extraordinary (X-) and ordinary (O-) mode linear polarizations. The amplitudes of the X-mode and O-mode signals are similar, which can be explained by depolarised reflected radiation. V-ECE measurements in low-density flattop discharges and in discharges with massive gas injections of high-Z elements show correlations with other RE diagnostics. Our results are in the agreement with the principles of the primary runaway generation mechanisms

Overview of the COMPASS results

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