Demonstration of soot Particle Resizing in an Ethylene Flame by Small Angle X-Ray Scattering

International audienceThe size distribution of soot nanoparticles in an ethylene flame has been mapped in an in situ small angle x-ray scattering measurement at the European Synchrotron Radiation Facility. It has been seen that an abrupt size distribution change occurs at about a third of the flame's visible height and this is believed to be due to the oxidation and dehydrogenation of the particles

First experimental determination of the absolute gas-phase rate coefficient for the reaction of OH with 4-hydroxy-2-butanone (4H2B) at 294 K by vapor pressure measurements of 4H2B.

International audienceThe reaction of the OH radicals with 4-hydroxy-2-butanone was investigated in the gas phase using an absolute rate method at room temperature and over the pressure range 10-330 Torr in He and air as diluent gases. The rate coefficients were measured using pulsed laser photolysis (PLP) of H(2)O(2) to produce OH and laser induced fluorescence (LIF) to measure the OH temporal profile. An average value of (4.8 ± 1.2) × 10(-12) cm(3) molecule(-1) s(-1) was obtained. The OH quantum yield following the 266 nm pulsed laser photolysis of 4-hydroxy-2-butanone was measured for the first time and found to be about 0.3%. The investigated kinetic study required accurate measurements of the vapor pressure of 4-hydroxy-2-butanone, which was measured using a static apparatus. The vapor pressure was found to range from 0.056 to 7.11 Torr between 254 and 323 K. This work provides the first absolute rate coefficients for the reaction of 4-hydroxy-2-butanone with OH and the first experimental saturated vapor pressures of the studied compound below 311 K. The obtained results are compared to those of the literature and the effects of the experimental conditions on the reactivity are examined. The calculated tropospheric lifetime obtained in this work suggests that once emitted into the atmosphere, 4H2B may contribute to the photochemical pollution in a local or regional scale

The far infrared spectrum of naphthalene characterized by high resolution synchrotron FTIR spectroscopy and anharmonic DFT calculations.

International audienceUsing synchrotron radiation, we performed the rotationally resolved Fourier transform infrared absorption spectroscopy of three bands of naphthalene C10H8, namely ν46-0 (centered at 782 cm(-1), 12.7 μm), ν47-0 (centered at 474 cm(-1), 21 μm), and ν48-0 (centered at 167 cm(-1), 60 μm). The intense CH bending out of plane ν46-0 band was recorded under supersonic jet-cooled conditions using a molecular beam (the Jet-AILES apparatus) and the low frequency ν47-0 and ν48-0 bands were measured at room temperature in a long absorption path cell. The simultaneous rotational analysis of these bands permitted us to refine the ground state (GS) and ν46 rotational spectroscopic constants and to provide the first sets of constants for the ν47 and ν48 modes. The experimental rotational constants were then used as reference data to calibrate theoretical models in order to provide new insights into the accuracy of anharmonic calculations. The B97-1 functional associated with the cc-pVTZ and ANO-RCC basis sets gave a consistent set of results, for rotational constants and fundamental frequencies. The data presented here pave the way for the search of naphthalene through its far-infrared spectrum in different objects of the interstellar medium

A New Instrument For Kinetics and Branching Ratio Studies of Gas Phase Collisional Processes at Very Low Temperatures

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A new instrument for kinetics and branching ratio studies of gas phase collisional processes at very low temperatures

International audienceA new instrument dedicated to the kinetic study of low-temperature gas phase neutral-neutral reactions, including clustering processes, is presented. It combines a supersonic flow reactor with vacuum ultra-violet synchrotron photoionization time-of-flight mass spectrometry. A photoion-photoelectron coincidence detection scheme has been adopted to optimize the particle counting efficiency. The characteristics of the instrument are detailed along with its capabilities illustrated through a few results obtained at low temperatures (<100 K) including a photoionization spectrum of n-butane, the detection of formic acid dimer formation, and the observation of diacetylene molecules formed by the reaction between the C2H radical and C2H2. © 2021 Author(s)