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Detection of astrochemically relevant reaction products in ...
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Skimmed CRESU setup ► Comparison of a vinyl cyanide FID and spectrum taken under the skimmer and the CRESU conditions highlights the power of the skimmer. The results from the skimmer chamber give longer FID and show an improvement of the SNR ► To improve the sensitivity of the technique, the CRESU flow is sampled via a skimmer into a new probing chamber under constant pumping ► The gas re-expands into a nearly collision free environment ► The pressure in the skimmer chamber can be lowered by orders of magnitude depending on the skimmer orifice, the flow conditions and the nature of the buffer ► The characterization of the post-skimmer expansion conditions was conducted via direct simulation Monte-Carlo (DSMC) calculations using DS2V program (Bird 1994) Detection of astrochemically relevant reaction products in skimmer sampled uniform supersonic flows using chirped pulse Fourier transform mm-wave spectroscopy Omar Abdelkader Khedaoui, Brian M. Hays, Ilsa R. Cooke, Thomas S. Hearne, Théo Guillaume, Divita Gupta, Myriam Drissi, Ian R. Sims Univ Rennes, CNRS, IPR (Institut de Physique de Rennes) - UMR 6251, F-35000 Rennes, France ► CRESU (Reaction Kinetics in Uniform Supersonic Flow) technique is coupled with the Chirped Pulse Fourier Transform Micro-(mm-)Wave (CPFTMW) spectroscopy technique ► Aim is to study low temperature gas phase collisional processes and determination of branching ratios of multichannel reactions in the interstellar medium CRESU Technique Transfer of heat to kinetic energy through an isentropic expansion of a gas via a convergent-divergent Laval nozzle creating a low temperature flow with uniform conditions 15 minutes 2 minutes CRESU Chamber Skimmer Chamber Pressure mbar Pressure μbar CRESU flow Expansion in the skimmer ► The skimmer geometry and its support are designed to avoid any perturbations of the CRESU flow conditions before reexpanding into the skimmer chamber ► CFD simulations were carried out to optimize the skimmer support profile ► The rotation diagram was made from a vinyl cyanide spectrum recorded from a chirp in the skimmer chamber to experimentally measure the rotational temperature of the gas expanding from an argon flow at 35 K ► Probing of HC 3 N as a product from the photolysis of vinyl cyanide at 193 nm in an argon flow at 35 K sampled via a 4 mm skimmer ► Two reactions have been studied, CN+C 2 H 2 a single channel reaction that yields HC 3 N as a product. The second is CN+C 2 H 4 which is potentially a dual channel reaction with vinyl cyanide from the first channel and HCN from the second channel used as probing molecules 193 nm laser Uniform flow Experimental Results Figure 5. CFD simulation of CRESU flow before expanding in the skimmer chamber Figure 6. DSMC simulation of the flow conditions in the skimmer chamber Figure 7. Rotation diagram from vinyl cyanide spectrum under skimmer conditions Figure 10. HC 3 N time dependent signal from CN+C 2 H 2 Figure 11. Vinyl cyanide time dependent signal from CN+C 2 H 4 Nozzle CRESU chamber Skimmer chamber Figure 8. Comparison of vinyl cyanide spectrum and FID under CRESU and skimmer conditions Figure 9. Photolysis of vinyl cyanide Pressure broadening ► Relatively high pressure generated in the CRESU flow ► High collision rate between the radiating molecules and the buffer gas ► Quenched FIDs and weak molecular signal Figure 4. skimmer chamber Figure 3. Vinyl cyanide FIDs and associated spectra with increasing pressures in a helium flow at room temperature Figure 2. Chirped-pulse technique Uniform flow Expansion Chirped pulse ► Excitation of dipole molecules within the frequency range of the pulse ► Record the free induction decay (FID) ► Fourier transform of the FID gives the spectrum Increase the pumping efficiency by pulsing the CRESU flow via an aerodynamic chopper The gain on pressure is determined by the geometry of the disk Spectroscopic probing in the reaction environment Future work We thank all the researchers and engineers of the Astrolab group in the institute of physics of Rennes particularly Jonathan Courbe and Abdessamad Benidar and also the technicians who helped build the skimmer chamber . The authors acknowledge funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement 695724-CRESUCHIRP). They are also grateful for support for the CRESUCHIRP project from PCMI, the European Regional Development Fund, Rennes Metropole and Region de Bretagne. Figure 1. Temperature profile from isentropic expansion Acknowledgments Introduction Skimmed CRESU setup
Transcript of Detection of astrochemically relevant reaction products in ...
Skimmed CRESU setup
►Comparison of a vinyl cyanide FID and spectrum taken under the skimmer and the
CRESU conditions highlights the power of the skimmer. The results from the
skimmer chamber give longer FID and show an improvement of the SNR
► To improve the sensitivity of the technique, the CRESU flow is sampled via a skimmerinto a new probing chamber under constant pumping
► The gas re-expands into a nearly collision free environment
► The pressure in the skimmer chamber can be lowered by orders of magnitudedepending on the skimmer orifice, the flow conditions and the nature of the buffer
► The characterization of the post-skimmer expansion conditions was conducted viadirect simulation Monte-Carlo (DSMC) calculations using DS2V program (Bird 1994)
Detection of astrochemically relevant reaction products in skimmer sampled uniform supersonic flows using chirped pulse Fourier transform mm-wave spectroscopy
Omar Abdelkader Khedaoui, Brian M. Hays, Ilsa R. Cooke, Thomas S. Hearne, Théo Guillaume, Divita Gupta, Myriam Drissi, Ian R. Sims
Univ Rennes, CNRS, IPR (Institut de Physique de Rennes) - UMR 6251, F-35000 Rennes, France
► CRESU (Reaction Kinetics inUniform Supersonic Flow)technique is coupled with theChirped Pulse Fourier TransformMicro-(mm-)Wave (CPFTMW)spectroscopy technique
► Aim is to study low temperaturegas phase collisional processes anddetermination of branching ratiosof multichannel reactions in theinterstellar medium
CRESU Technique
Transfer of heat to kinetic energythrough an isentropic expansion of a gasvia a convergent-divergent Laval nozzlecreating a low temperature flow withuniform conditions
15 minutes
2 minutes
CRESU Chamber
Skimmer Chamber
Pressure mbar
Pressure μbar
CRESU flow Expansion in the skimmer
► The skimmer geometry and its support
are designed to avoid any perturbations
of the CRESU flow conditions before
reexpanding into the skimmer chamber
► CFD simulations were carried out to
optimize the skimmer support profile
► The rotation diagram was made from a vinyl cyanide spectrum recorded from a chirpin the skimmer chamber to experimentally measure the rotational temperature of thegas expanding from an argon flow at 35 K
► Probing of HC3N as a product fromthe photolysis of vinyl cyanide at193 nm in an argon flow at 35 Ksampled via a 4 mm skimmer
► Two reactions have been studied, CN+C2H2 a single channel reaction that yields HC3N asa product. The second is CN+C2H4 which is potentially a dual channel reaction with vinylcyanide from the first channel and HCN from the second channel used as probingmolecules
193 nm laser
Uniform flow
Experimental Results
Figure 5. CFD simulation of
CRESU flow before expanding
in the skimmer chamber
Figure 6. DSMC simulation of the flow conditions in the skimmer chamber
Figure 7. Rotation diagram from vinyl cyanide spectrum under skimmer conditions
Figure 10. HC3N time dependent signal from CN+C2H2
Figure 11. Vinyl cyanide time dependent signal from CN+C2H4
NozzleCRESU
chamberSkimmer chamberFigure 8. Comparison of vinyl cyanide spectrum and
FID under CRESU and skimmer conditions
Figure 9. Photolysis of vinyl cyanide
Pressure broadening
► Relatively high pressure generated inthe CRESU flow
► High collision rate between theradiating molecules and the buffer gas
► Quenched FIDs and weak molecularsignal
Figure 4. skimmer chamber
Figure 3. Vinyl cyanide FIDs and associated spectra with increasing
pressures in a helium flow at room temperature
Figure 2. Chirped-pulse technique
Uniform flowExpansion
Chirped pulse
► Excitation of dipolemolecules within thefrequency range of the pulse
► Record the free inductiondecay (FID)
► Fourier transform of the FIDgives the spectrum
Increase the pumping efficiency by pulsing the CRESUflow via an aerodynamic chopper
The gain on pressure is determined by the geometryof the disk
Spectroscopic probing in the reaction environment
Future workWe thank all the researchers and engineers of the Astrolab group in the institute of physics of Rennes particularlyJonathan Courbe and Abdessamad Benidar and also the technicians who helped build the skimmer chamber . Theauthors acknowledge funding from the European Research Council (ERC) under the European Union’s Horizon 2020research and innovation program (grant agreement 695724-CRESUCHIRP). They are also grateful for support for theCRESUCHIRP project from PCMI, the European Regional Development Fund, Rennes Metropole and Region deBretagne.
Figure 1. Temperature profile from isentropic expansion
Acknowledgments
Introduction
Skimmed CRESU setup
