Workshop REACPLASJean-Christophe Loison (ISM, CNRS - Univ. Bordeaux I, Bordeaux, France) 17:10 –...

Workshop

Reactivity, Plasmas, Astrophysics Processus collisionnels et réactivité d’espèces transitoires en phase gazeuse -

Aspects élémentaires et Applications aux Plasmas Froids et Astrophysiques

http://www.lcp.u-psud.fr/spip.php?article550

Mardi 21 novembre 2017 Laboratoire de Chimie Physique

Bât 349, Université Paris-Sud, Orsay

REACPLAS

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Workshop rEACpLAs (phoM rEsEArCh sEMinAr)

Collisional processes and reactivity of transient species in the gas phase: From Elementary processes to Applications for Cold plasmas and Astrophysics

processus collisionnels et réactivité d’espèces transitoires en phase gazeuse - Aspects élémentaires et Applications aux plasmas Froids et Astrophysiques

We are pleased to announce the REACPLAS workshop, in the series of PhOM Re-search Seminars, aiming to bring together specialists (in both experiment and theory) of reactivity and elementary collisional processes in the gas phase with modellers of complex media (such as cold plasmas, planetary atmospheres or interstellar media) whose composition and dynamics are driven by these elemen-tary processes. The objective is to exchange knowledge on the available tools and to identify the important processes necessary occurring in these media that are not yet well characterized and that are in need of further investigation which could benefit from new collaborations.

orgAnizing CoMMittEE

- Christian Alcaraz (LCP) - [email protected] Jean-Paul Booth (LPP) - [email protected] Gilles Maynard (LPGP) - [email protected] ève Ranvier (LCP) - [email protected] Élodie Van-Cracynest (LCP) - [email protected]

ACknoWLEdgEMEnts

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Workshop REACPLAS (PhOM Research Seminar) Tuesday 21 november 2017

Laboratoire de Chimie Physique (LCP), Bât 349, Université Paris-Sud, Orsay

Collisional processes and reactivity of transient species in the gas phase: From Elementary Processes to Applications for Cold Plasmas and Astrophysics

Processus collisionnels et réactivité d'espèces transitoires en phase gazeuse – Aspects élémentaires et Applications aux Plasmas Froids et Astrophysiques

1/ PROGRAM OF TALKS

08:50 – 09:00: Introduction

Chairman: Pascal Pernot 09:00 – 09:35: “Ion-molecule reactions of relevance in astrochemistry and laboratory plasmas”

Daniela Ascenzi (Dept. of Physics, University of Trento, Italy)

09:35 – 10:10: “Reaction Chemistry in Atmospheric Pressure Plasmas” Achim von Keudell (Fak. für Physik und Astronomie, Ruhr-Universität Bochum, Germany)

09:10 – 10:30: “Mass spectrometry in a N2-H2 CCP RF discharge partially representative of Titan’s ionosphere” Audrey Chatain (LATMOS, UVSQ-CNRS, Guyancourt & LPP, École X -CNRS, Palaiseau, France)

10:30 – 11:00: Coffee Break and Posters

Chairman: Jean-Paul Booth 11:00 – 11:35: “Electron-electron coincidence studies of double ionisation of small systems”

Elena-Magdalena Staicu Casagrande (ISMO, Univ. Paris-Sud & Saclay, Orsay, France)

11:35 – 12:10: “Cross sections for electron collisions with molecules leading to excitation and dissociation” Jimena Gorfinkiel (Open University, Milton Keynes, United Kingdom)

12:10 – 12:30: “Reactive collisions of electrons with molecular cations: mechanisms, cross section production and applications to cold ionized media modeling” Ioan F. Schneider (LOMC, CNRS-U. du Havre & LAC, CNRS - ENS Cachan - U. Paris-Sud, France)

12:30 – 14:00: Lunch and Posters

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Chairman: Gilles Maynard 14:00 – 14:35: “Kinetics of organic molecules in pulsed plasmas. Applications for pollution control and combustion

triggering” Stéphane Pasquiers (LPGP, CNRS - U. Paris-Sud & Saclay, Orsay, France)

14:35 – 15:10: “Reactivity, relaxation and dissociation of molecules in plasma modelling” Fabrizio Esposito (Plasmi Lab @ Nanotec, CNR, Bari ,Italy)

15:10 – 15:30: “Kinetics of pulsed discharges under conditions of high electric field and high deposited energy” Svetlana Starikovskaia (LPP, CNRS - Ecole Polytechnique - Sorbonne U. - UPMC-Paris 6 - U. Paris-Sud, U. Paris-Saclay, Palaiseau, France)

15:30 – 16:00: Coffee Break and Posters

Chairman: Roland Thissen 16:00 – 16:35: “Dissociative Recombination: Where are we experimentally ?”

J. Brian A. Mitchell (Merl-Consulting, Rennes, France)

16:35 – 17:10: “Isotopic fractionation: 15N and 13C exchange reactions” Jean-Christophe Loison (ISM, CNRS - Univ. Bordeaux I, Bordeaux, France)

17:10 – 17:30: “Ion chemistry at low temperature with supersonic flows” Ludovic Biennier (IPR, CNRS – U. Rennes 1, Rennes)

17:30 – 18:30: General Discussion

2/ PROGRAM OF POSTERS

Poster 1: “Kinetics of metastable states and atoms in DC discharges in pure O2: an experimental study”

Jean-Paul Booth & Abhyuday Chatterjee (LPP, CNRS - Ecole Polytechnique - Sorbonne U. - UPMC-Paris 6 - U. Paris-Sud & Paris-Saclay, Observatoire de Paris, Palaiseau & Synchrotron SOLEIL, St Aubin , France)

Poster 2: “Acetone decomposition kinetics in plasmas of N2/O2 mixtures” Nicole Blin-Simiand (LPGP, CNRS - U. Paris-Sud & Saclay, Orsay, France)

ORGANIZING COMMITTEE - Christian Alcaraz (LCP) - Jean-Paul Booth (LPP) - Gilles Maynard (LPGP)

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ABstrACts oF invitEd tALks

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REACPLAS

Ion-molecule reactions of relevance in astrochemistry

and laboratory plasmas Daniela Ascenzi

Department of Physics, University of Trento, Italy Physical and chemical processes involving atomic and molecular ions occur in many gaseous and plasma environments, where high energy particles or photons are present to provide ionization of neutrals. Natural environments where ion-molecule interactions play a role range from the ionospheres of planets and satellites, to interstellar and circumstellar regions and gas clouds, to flames and combustion systems, but charged species are also relevant in electrical discharges and laboratory plasmas for technological applications (e.g. discharge lamps, plasmas for etching, film deposition and surface modifications, nanosecond repetitively pulsed discharges for energetic and environmental applications). Ion-molecule reactions participate to the balance and redistribution of charges in the above mentioned systems, as well as to the synthesis/destruction of chemical species. Hence a detailed knowledge of reaction kinetics and dynamics of ion-molecule systems is fundamental for a correct modelling of such complex environments. Our contribution is in the laboratory measurements of kinetic parameters (cross sections, branching ratios and their dependences on collision energy) for the reaction of charged molecules with neutrals, by using tandem mass spectrometric techniques and RF octupolar trapping of parent and product ions. In some cases, photoionization via synchrotron radiation is used to attain isomer selectivity or to generate cations with a controlled amount of internal energy. In this presentation I will review some of our recent results that contributed to shed lights on the growth and destruction processes of nitrogen and oxygen containing organic molecules. If time permits I will give also a brief overview of the activity carried out in Trento on the diagnostics, kinetics and chemistry of high pressure electrical discharges. Acknowledgments

All the members and collaborators of the Molecular Physics group at Trento University are kindly acknowledged: Paolo Tosi, Luca M. Martini, Andrea Cernuto, Giorgio Dilecce, Mario Scotoni, Sara Lovascio, Nicola Gatti. The work here presented is the result of an extensive collaboration between our group at Trento University and other research groups: Christian Alcaraz, Claire Romanzin, Roland Thissen (Univ. Paris Sud et Paris-Saclay, FR), Wolf Geppert & Pantea Fathi (Stockholm University), Miroslav Polasek & Jan Zabka (Heyrovsky Institute of Physical Chemistry, Prague), Cecilia Ceccarelli (IPAG Grenoble), Fernando Pirani & Nadia Balucani (Univ. Perugia), Glauco Tonachini & Andrea Maranzana (Univ. Turin, IT).

Reaction Chemistry in Atmospheric Pressure Plasmas

Achim von Keudell

Institute for experimental Physics II, Reactive Plasmas Ruhr University Bochum, Bochum, Gemany

Non-‐equilibrium atmospheric pressure plasmas gained huge interest over the past decade due to their easy integration with other process technologies. However, numerous physical questions need to be addressed to control the reaction chemistry and to reach a stable homogeneous atmospheric pressure non-‐equilibrium plasma: How can the instabilities of these atmospheric pressure plasmas be mastered? How is the coupling and coupling-‐out of particles, radiation and energy in these systems realized? How can the plasma chemistry and the gas flow self-‐consistently treated in modeling? How need classical diagnostic concepts to measure standard plasma parameters such as electron density or temperature to be adapted at atmospheric pressure to be reliable? In all of these questions, we are currently reaching the limits of the possibilities of experiment, theory and simulation. In this contribution, the basic concepts and questions of the very hot topic of cold atmospheric pressure plasmas will be explained and several relevant reaction mechanisms will be highlighted.

ELECTRON-ELECTRON COINCIDENCE STUDIES OF DOUBLE IONIZATION

OF SMALL SYSTEMS

Elena Magdalena Staicu Casagrande

The study of multiple ionization processes by charged particle impact is of considerable

interest not only in physics but also in life sciences where it is of prime importance to

understand the various mechanisms leading to energy deposition by radiation in matter.

Electron impact double ionization (DI) is one of the most fundamental of such

processes. The advent of multi-parameter detection techniques has made it possible to

perform complete experiments in which all kinematical parameters (vector momenta

and energies) of all involved particles are determined. These so-called (e,3e)

experiments have been used during the last two decades to investigate in very fine

details the various projectile – target interaction mechanisms leading to the DI process.

We have performed (e,3e) experiments as well as their simplified form denoted (e,3-1e)

for the double ionization of helium and hydrogen molecule in coplanar asymmetric

geometry for a wide range of ejected electron energies. From the usual forward and

backward lobes, they reported unprecedently observed additional structures in the

angular distributions of the ejected electrons issued from DI. A classical kinematical

model was there proposed to interpret the most preeminent additional structures as

being due to two consecutive collisions of the projectile electron with the target (the so-

called two-step 2 mechanism, TS2), each of these collisions being modeled by a single

ionization (SI) binary (e,2e) process.

These results were generalized to other rare gas atoms (Ne, Ar) and to molecules (N2,

CH4). By including to the previous kinematical model the recoil contributions from the

two considered SI (e,2e) processes, we were able to demonstrate that most of the

observed structures are due to a TS2 mechanism for DI, and that they can be related to

particular combinations ‘binary-binary’ or ‘recoil-recoil’ scattering during the two

successive (e,2e) SI events

The success of the proposed classical kinematical two-step model leads to conclude that

DI is largely dominated by the TS2 mechanism under the considered kinematics.

C Li, A Lahmam-Bennani, E M Staicu Casagrande and C Dal Cappello J. Phys. B: At. Mol. Opt. Phys. 45

135201(2012)

E M Staicu Casagrande, C Li, A Lahmam-Bennani and C Dal Cappello J. Phys.B : At. Mol. Opt. Phys 47

(2014) 115203

Cross sections for electron collisions with molecules leading to excitation and dissociation

Jimena D. Gorfinkiel

School of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, United Kingdom

E-mail: [email protected]

Electron collisions with molecules occur in many environments (many with technological applications): cool plasmas and discharges, Earth’s atmosphere, planetary auroras and weakly ionized areas of the interstellar medium, etc.. In addition, low-energy electron collisions are a major cause of radiation damage within cells, and therefore of great interest to biomedicine, as radiation is used both for disease treatment and imaging. The importance of electron-molecule collisions, particularly at low energy, has stimulated significant work both experimentally and theoretically over the last decade. In my talk, I will concentrate on one of the most widely used theoretical tools, the R-matrix method. The R-matrix method [1] is an ab initio variational solution to the time-independent Schrödinger equation for electron and positron scattering from atoms/ions, molecules and molecular clusters. The treatment of electron/positron collisions with molecules using the R-matrix method has been implemented in the UKRmol and UKRmol+ suites [2,3]. Recent developments of these suite have significantly improved their efficiency and added new functionality, enabling the study of electron scattering for bigger and more electron-rich molecules than ever before. These developments are also enabling more accurate calculations for smaller targets, particularly for electronic excitation [4]. Recent work at The Open University using the UKRmol/UKRmol+ suites has concentrated on

systems of biological relevance and clusters of a biomolecule and a small number of water molecules [5]. The study of electron collisions with these clusters have enabled us to start developing an understanding the effect that microhydration has on the outcome of the collisions. I will discuss these and other and recent developments and results that ilustrate the type and quality of caculations that can currenty be performed. [1] Burke, P.G., 2011, R-matrix Theory of Atomic Collisions: Application to Atomic, Molecular

and Optical Processes. Springer; J. Tennyson, 2010, Physical Reports 491, 29.

[2] http://ccpforge.cse.rl.ac.uk/gf/project/ukrmol-in/, /ukrmol-out/

[3] Carr, J.M. et al., 2012, Eur. Phys. J. D 66, 58-69.

[4] Regeta K. et al., 2016, JCP 144, 024302

[5] A. Loupas and J. D. Gorfinkiel, 2017, PCCP 19, 18252; A. Sieradzka and J.D. Gorfinkiel,

2017, JCP 147, 034302.

Workshop REACPLAS (PhOM Research Seminar) - Tuesday 21 november 2017 Laboratoire de Chimie Physique (LCP), Bât 349, Université Paris-Sud, Orsay

Kinetics of organic molecules in pulsed plasmas Applications for pollution control and combustion triggering

S. Pasquiers, N. Blin-Simiand, L. Magne

Laboratoire de Physique des Gaz et des Plasmas

Univ. Paris-Sud, CNRS (UMR8578), Univ. Paris-Saclay

For more than twenty years, numerous works were undertaken on the treatment of gaseous

effluents containing organic pollutants emitted by human activities, hydrocarbons (HCs) and

Volatile Organic Compounds (VOCs), by non-thermal plasmas. Most of these works deal

with oxygenated VOCs belonging to several chemical families such as aldehydes

(formaldehyde, acetaldehyde), ketones (acetone), alcohols (ethanol, isopropanol), etc...

Aliphatic (ethane, ethane, propene, propane) and aromatic (benzene, toluene) hydrocarbons

are also considered. Nevertheless, few studies focus on a detailed description of the kinetics

of these molecules in the mixture of atmospheric gases (N2, O2, H2O). The plasmas are often

produced by pulsed electrical discharges (corona, dielectric barrier, pre-ionised…) of short

duration (< 100 ns), wherein a complex molecular kinetics takes place. Discharges can be

coupled to catalysis in order to achieve the best energy efficiency for the total oxidation of the

pollutants. Many compounds should be produced owing to the decomposition of the primary

pollutant, which must be further oxidized by adequate catalysts. However, a comprehensive

description of the HC-VOCs kinetics in the plasma phase is always needed for the process

optimization. Accurate knowledge of the degradation kinetics of HC-VOCs would make it

possible to more confidently predict, by modeling, the energy performance of a treatment

reactor and to optimize its characteristics without resorting to numerous experimental

parametric studies. About aliphatic HCs, works on combustion triggering and control have

motivated more detailed kinetic studies, but uncertainties remain about secondary species,

molecules and radicals, coming from decomposition of the primary molecule.

The kinetics of HCs and VOCs can be particularly complex, depending on the type of

discharge used to create the plasma and the concentrations of molecules in the gas mixture. It

depends also a lot on the chemical nature of the organic. The oxidation by O or by OH,

produced by O2 and H2O dissociation, are important processes. However oxidation reactions

can be dominated by the quenching of excited electronic states of nitrogen, N2*, excitation

transfer processes towards the organic molecule inducing its dissociation into multiple

fragments. The competition between oxidation and dissociation in organic degradation is a

current subject of study, but with many unknowns, in particular: i/ the reaction coefficient of

N2* with the molecule, ii/ the nature of the radicals and molecules produced directly by

dissociation and their respective branching rates, iii/ the reaction of the organic with the

metastable state O(1D), first excited state of O. For many molecules the oxidation by the

ground state O(3P) and by OH have been the subject of many studies, but there is little data on

O(1D). However it is known, for some compounds, that the reaction coefficient at room

temperature (293 K) is several orders of magnitude higher than that of O(3P). It should also be

mentioned that the few published works on the role of dissociations concern the metastable

states of N2 (A3

+u and singlets a'

1

-u, a

1g, and w

1

u), but nothing is known about the low-

energy radiative states (B3g, W

3u, B'

3

-u, and C

3u) whose densities, for some discharges,

may be comparable or even greater than those of metastables. Other kinetic processes are also

likely to occur in the degradation of HC-VOCs, for which very few data exist: i/ non-ionizing

collisions with the electrons producing dissociative electronic states of the molecule, ii/

reactions of the molecule with the majority ions (N2+, O2

+, N4

+, O4

+).

Our research team (Dirébio) at LPGP has been involved in these topics for the past ten years,

and is currently working with partners from LCP (RISMAS).

Reactivity, relaxation and dissociation of molecules in plasma modelling

Fabrizio Esposito

Consiglio Nazionale delle Ricerche, P.LAS.M.I.Lab@Nanotec, Bari, Italy

The role of molecular vibration in non-‐equilibrium plasma modelling is nowadays well recognized in the literature [1]. The internal energy of molecules acts as a sort of energy bank, which can store and release energy with specific processes (collisions with other molecules and with electrons, radiation) and characteristic times, and these processes have strong influence on the overall kinetics. A state-‐to-‐state kinetic model includes not simply the chemical species participating in a phenomenon, but also their behaviour as a function of their internal energy. In order to perform this kind of accurate modelling there is the need of detailed data, concerning in particular molecular collision (reactive, inelastic and dissociation/recombination processes), in the form of rate coefficients or cross sections depending on initial and final molecular vibration. Experimental data with this level of detail are scarce and generally limited to very few vibrational states. In the past the input data of vibrational kinetics were obtained by using simple models of vibrational energy transfer, based essentially on a forced harmonic oscillator model. However, this model makes sense for low vibrational energy transitions, and for "purely" inelastic processes [2]. When the collisional system includes one or more reactive channels, the vibrational kinetics of inelastic processes can be significantly different if the reaction threshold is approached or not [3]. Molecular dynamics calculations can give valuable contributions to the solution of these issues. Different methods are available, with different levels of accuracy and requirements of computational resources. However, when dealing with modelling, complete sets of rate coefficients (in the sense of including the whole vibrational ladders of both reagents and products) are required, with ranges of collision energy normally quite large. As a consequence, the only possible strategy should be to merge results from different methods. This has been done in [4], where reaction of light species as a function of initial and final vibration is very accurately reproduced using quasiclassical trajectory method in comparison with accurate time independent quantum mechanical calculations. Also vibration-‐dependent dissociation/recombination of light species can be studied using quasiclassical trajectories, provided the results of direct three-‐body and of orbiting resonance theory are correctly merged [5]. Also in this case good comparisons are obtained with quantum mechanical results. What emerges from all these comparisons of quite different vibrational processes is the importance of studying the correct and convenient limits of application of each dynamical method, in order to obtain the best performance by each method and to merge all the results into a consistent collection of data for modelling. References (1) Capitelli, M.; Armenise, I.; Bisceglie, E.; Bruno, D.; Celiberto, R.; Colonna, G.; D’Ammando, G.; De

Pascale, O.; Esposito, F.; Gorse, C.; et al. Thermodynamics, Transport and Kinetics of Equilibrium and Non-‐Equilibrium Plasmas: A State-‐to-‐State Approach. Plasma Chem. Plasma Process. 2012, 32 (3), 427–450.

(2) Capitelli, M.; Celiberto, R.; Colonna, G.; Esposito, F.; Gorse, C.; Hassouni, K.; Laricchiuta, A.; Longo, S. Reactivity and Relaxation of Vibrationally/Rotationally Excited Molecules with Open Shell Atoms. In Fundamental Aspects of Plasma Chemical Physics; Springer Series on Atomic, Optical, and Plasma Physics; Springer New York, 2016; Vol. 85, pp 31–56.

(3) Esposito, F.; Armenise, I. Reactive, Inelastic, and Dissociation Processes in Collisions of Atomic Oxygen with Molecular Nitrogen. J. Phys. Chem. A 2017, 121 (33), 6211–6219.

(4) Esposito, F.; Coppola, C. M.; De Fazio, D. Complementarity between Quantum and Classical Mechanics in Chemical Modeling. The H + HeH+ → H2+ + He Reaction: A Rigourous Test for Reaction Dynamics Methods. J. Phys. Chem. A 2015, 119, 12615−12626.

(5) Esposito, F.; Capitelli, M. Selective Vibrational Pumping of Molecular Hydrogen via Gas Phase Atomic Recombination. J. Phys. Chem. A 2009, 113, 15307–15314.

"Dissociative Recombination: Where are we experimentally?"

J. Brian A. Mitchell

Merl-Consulting, Rennes France

([email protected]) Dissociative recombination (DR) where a molecular ion recombines with an electron, becomes neutralised and dissociates, carrying away the excess recombination energy, is a process which is important for the chemistry of environments which contain such molecular ions such as interstellar clouds, materials processing plasmas and fusion walls and diverter plasmas.

Our knowledge of this process comes from experimental measurements backed up by theoretical predictions, but because of the complexity of the process, neither can be said to fully cover the mechanisms involved. The role of the infinite number of Rydberg states lying beneath the ion ground state, through which the recombining system must interact and pass, makes our understanding of the capture and subsequent dissociation process approximate for all but the simplest cases (whatever these may be). The complication of initial ro-vibrational states of the recombining ions, adds to this complication. Modern experiments and theoretical approaches have made great progress is dealing with these complications with state control in heavy ion storage rings and greater understanding of capture process for diatomic (and even simple polyatomic systems). However, theoretical approaches have largely failed to increase our knowledge of dissociation pathways which release reactive radical species into the molecular environment. Storage ring experiments have been able to study this aspect and have provided valuable information in particular as to how polyatomic molecules break-up when recombining, showing that unlike what is often supposed in chemical models, this is not just the hiving off of a light molecule such as a hydrogen atom in the case of hydrocarbon species.

The recombination of species which are easily undergoing clustering reactions is another aspect of DR where early experiments have led to much confusion and where efforts have been made to try to explain measured recombination rates which in some cases have found very high values.

There is clearly much to be done. The current status of the field from an experimental point of view is not rosy however, as the heavy ions storage rings which spearheaded the advances have all now closed. While we await new machines, the only results in recent years have come from afterglow experiments. Here we have seen in recent experiments, that these have what seems to be a fundamental limit when we try to study species where the neutral molecules turn out to themselves capture electrons.

In my talk I shall review the current status as I understand it and shall try to predict what we are likely to see in the coming years.

Isotopic fractionation: 15N and 13C exchange reactions Jean-Christophe Loison

Understanding isotopic abundances on a large scale (terrestrial environments (ocean, meteorites), the solar system (planets, comets), and galactic interstellar space) may give us some information about the link between solar system objects and galactic interstellar environments. Among the various fractionation, nitrogen one is one of the most puzzling one. (Terzieva & Herbst 2000) in a pioneering study proposed various 15N isotopic exchange reactions. However, for most of them there was no information on these reactions and we performed DFT calculations to get a clearer picture. Furthermore, various species such as H12CN and HN12C, show optically thick lines and HC15N and H15NC relative abundances are calculated with respect to observations of H13CN and HN13C isotopomers using a 12C/13C ratio of between 64 and 68, the most recent estimation being 68 (Milam et al. 2005). The results are reliable only if species do not undergo significant carbon fractionation. I will present in my talk a review of the possible isotopic exchange reactions that are involved for molecules containing carbon and nitrogen. Milam S.N., Savage C., Brewster M.A., et al., 2005, ApJ, 634 Terzieva R., Herbst E., 2000, Monthly Notices of the Royal Astronomical Society, 317, 563

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ABstrACts oF ContriButEd tALks

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REACPLAS

Workshop REACPLAS – 21st of november, 2017 – LCP, Orsay

MASS SPECTROMETRY IN A N2-H2 CCP RF DISCHARGE PARTIALLY REPRESENTATIVE OF TITAN’S IONOSPHERE

A. Chatain[1,2], N. Carrasco[1], O. Guaitella[2], L. Vettier[1], G. Cernogora[1]

[1] LATMOS, Université de Versailles St Quentin-en-Yvelines, CNRS, 78280 Guyancourt [2] LPP, École Polytechnique, CNRS, 91128 Palaiseau

[email protected] Abstract

Titan is a moon of Saturn well known for its thick orange atmosphere which contains lots of

organic aerosols. The Cassini spacecraft, which observed Titan from 2004 to 2017, discovered

that such aerosols start forming above 1200km, in the ionosphere [3]. At this altitude the

atmosphere is a N2-CH4-H2 dusty plasma (in respective proportions 98.4%-1.4%-0.2%). It is

the place of a complex chemistry leading to the formation of the aerosols. The plasma

conditions are also likely to modify them during their stay in the ionosphere.

To understand the different processes happening we experimentally simulate a simplified Titan

ionosphere in the reactor PAMPRE [2]. It is a stainless steel cylinder, of 30cm in diameter and

40cm in height, in which we can create a radio-frequency capacitively coupled plasma

discharge.

Pure N2 conditions have already been studied and modelled [1]. The aim of this work is to

characterize the effect of the addition of H2 in the plasma. Positive ions are especially

interesting to study as they give information on the plasma structure and should strongly

interact with aerosols that tend to charge negatively. Here we study the evolution of neutral and

positive ion populations by mass spectrometry.

We observe that ion populations radically change in favour of protonated ions with the addition

of hydrogen (even with only 0.1% of H2 in N2). However, these distributions stabilize for

amounts above 1% of H2. We also detect the formation of NH3. These measurements will enable

us to model the plasma inside PAMPRE, which will help to understand the processes happening

on Titan.

References

[1] Alves, L. L., Marques, L., Pintassilgo, C. D., Wattieaux, G., Es-Sebbar, E. T., Berndt, J., ... & Cernogora, G. (2012).

Capacitively coupled radio-frequency discharges in nitrogen at low pressures. Plasma Sources Science and

Technology, 21(4), 045008.

[2] Szopa, C., Cernogora, G., Boufendi, L., Correia, J. J., & Coll, P. (2006). PAMPRE: A dusty plasma experiment for

Titan's tholins production and study. Planetary and space Science, 54(4), 394-404.

[3] Waite, J. H., Young, D. T., Cravens, T. E., Coates, A. J., Crary, F. J., Magee, B., & Westlake, J. (2007). The process of

tholin formation in Titan's upper atmosphere. Science, 316(5826), 870-875.

We acknowledge the financial support of the European Research Council (ERC Starting Grant PRIMCHEM, Grant agreement no. 636829) and the École Normale Supérieure Paris-Saclay.

Reactive collisions of electrons with molecular cations: mechanisms, cross section production and applications to cold ionized media modeling

J. Zs. Mezei1,2,3,4, V. Laporta1, A. Abdoulanziz1 and I. F. Schneider1,3

P

1Laboratoire Ondes et Milieux Complexes, CNRS, Université du Havre, Le Havre, France 2Laboratoire des Sciences des Procédés et des Matériaux, CNRS, Université Paris 13, Villetaneuse, France

3Laboratoire Aimé Cotton, CNRS, ENS Cachan and Université Paris-Sud, Orsay, France 4Instititute of Nuclear Research of the Hungarian Academy of Sciences, Debrecen, Hungary

Electron-impact dissociative recombination (1), ro-vibrational excitation (2) and dissociative

excitation (3) [1]: AB+(Ni

+,vi+)+e-→AB*,AB**→A+B, (1)

→AB*,AB**→AB+(Nf+,vf

+)+e-, (2) →AB**→A+B++e-, (3) - AB* standing for Rydberg bound states and AB** for dissociative states - occur in various ionized media of astrophysical, energetic and industrial interest.

Being highly-reactive, involving super-excited molecular states undergoing predissociation and autoionization, and having a strong resonant character, these collisions are subject to beyond-Born-Oppenheimer theoretical approaches, and often require quasi-diabatic - rather than adiabatic -representations of the molecular states, as well as particularly sophisticated methods for modelling the fragmentation dynamics, able to manage the superposition of many continua.

A brief description of the methods we use to study these reactions will be given. The first one, based on the Multichannel Quantum Defect Theory (MQDT), is capable to

take into account the strong mixing between ionization and dissociative channels, open - direct mechanism - and closed - indirect mechanism, and the capture into infinite series of Rydberg resonances [2-4]. A second one, based on the Configuration Interaction method and the projector operators technique [5,6], is very efficient far from the Rydberg resonances region, and allows the approach of electron/neutral molecule collisions. And finally, our wave-packet approach [7] is meant to be developed in order to be applied to polyatomic systems and to branching ratios predictions.

Illustrations for H2+ [7-9], CH+ [10], CO+ [11], N2

+ [12], SH+ [13], H3+ [14] and ArH+ [15]

will be given, emphasising each time the implication in the kinetics of various ionized cold diluted media occurring in interstellar molecular clouds, early Universe, planetary atmospheres, plasma formed at the hypersonic entries of spacecrafts, edge fusion plasmas, and plasmas assisting combustion, depollution and industrial processes (ion implantation, etc.).

References [1] I. F. Schneider, O. Dulieu, and J. Robert (editors), 2015, Eur. Phys. J. Web of Conf. 84. [2] Ch. Jungen, 2011, in Handbook of High-resolution Spectroscopy, edited by M. Quack and F. Merkt (Wiley & Sons, New York), p.471. [3] A. Giusti, 1980, J. Phys. B: At. Mol. Phys. 13, 3867. [4] F. O.Waffeu Tamo et al, 2011, Phys. Rev. A 84, 022710. [5] V. Laporta et al, 2017, Plasma Phys. Contr. Fusion 59, 045008. [6] N. Bardsley, 1968, J. Phys. B 1, 349. [7] S. Morisset et al, 2007, Phys. Rev. A76, 042702. [8] O. Motapon et al, 2014, Phys. Rev. A 90, 012706. [9] K. Chakrabarti et al, 2013, Phys. Rev. A 87, 022702. [10] A. Faure et al, 2017, MNRAS 469, 612. [11] J. Zs. Mezei et al, 2015, Plasma Sources Sci. Technol. 24, 035005. [12] D. A. Little et al, 2014, Phys. Rev. A 90, 052705. [13] D. O. Kashinski et al, 2017, J. Chem. Phys. 146, 204109. [14] I. F. Schneider et al, 2012, Phys. Rev. A 86, 062706. [15] Mitchell J. B. A., et al., 2005, J. Phys. B: At. Mol. Phys. 38, L175.

Kinetics of pulsed discharges under conditions of

high electric field and high deposited energy

Nikita Lepikhin1, Georgy Pokrovskiy

1, Nikolay Popov

2, Svetlana Starikovskaia

1

1Laboratory of Plasma Physics (CNRS, Ecole Polytechnique, Sorbonne Universities,

University of Pierreand Marie Curie-Paris 6, University Paris-Sud), Ecole Polytechnique,

route de Saclay, 91128 Palaiseau, France 2Skobeltsyn Institute of Nuclear Physics, Moscow State University, Moscow, 119991,

Leninsky gory, Russia

Strongly non-equilibrium plasma at high electric fields and high specific deposited energy

was studied in capillary nanosecond discharge in 20 Torr N2:O2 mixtures. The discharge

developed in the quartz capillary with inner diameter 1.5 mm and length 80 mm. The capillary

was inserted into the break in the coaxial cable at the distance 25 m from the high-voltage

generator (FID FPG 10-MKS20 HV, FID GmbH). Pulses of 20 kV amplitude on the

electrode, 30 ns FWHM and 4 ns rise time were repeated with a frequency of a few Hz to

accumulate the signal; gas flow rate provided change of the gas in the capillary between two

pulses. Calibrated back current shunts where used to measure current, voltage in the cable and

energy stored in plasma. The electric field was measured by capacitive gauge and from optical

emission spectroscopy. For emission spectroscopy measurements, the Acton spectrometer

(SP-2500i, 1200 I/mm grating, Princeton Instrument) was combined with Pi-Max4 (Princeton

Instruments) ICCD camera. Two-photon absorption laser induced fluorescence (TALIF) was

used to measure O-atoms density in oxygen-containing mixtures in late afterglow (t<1000 ns).

Measured specific deposited energy in the discharge was as high as 0.5-1.0 eV/molecule, the

electric field on the stage of maximum energy deposition was in the range of 200-400 Td. It

was shown that kinetics in the discharge requires taking into account reactions of interaction

between charged/dissociated and excited species. High rates of quenching of electronically

excited species by electrons were observed in early afterglow [1]. Dissociation degree of

oxygen in the discharge reached tens of percent, increasing to 100% at microseconds due to

reactions between O2 and electronically excited nitrogen. Heating of the gas up to a few

thousand K was observed at the time scale less than VT-relaxation due to energy release in

reactions with electronically excited species. It was shown that in pure nitrogen, the heating is

comparable to heating in air, comprising about 2000 K during 1 miscosecond, although

kinetic paths are different.

Acknowledgments:

The work was partially supported by the French National Research Agency, ANR ASPEN

Project (ANR-16-CE30-0004-01), LabEx Plas@Par and Linked International Laboratory LIA

KaPPA (France-Russia), RFBR project 17-52-16001. The work of Georgy Pokrovskiy is

supported by PhD Saclay Doctoral Program.

[1] N.D. Lepikhin, A.V. Klochko, N.A. Popov, S.M. Starikovskaia, Plasma Sources Sci.

Tech., 25 (2016) 045003 (11pp)

Ion chemistry at low temperature with supersonic flows

Ludovic Biennier1, Nour Jamal-‐Eddine1, Baptiste Joalland1, Sophie Carles1, Jean-‐Claude Guillemin2, François Lique3

1 Institut de Physique de Rennes UMR CNRS 6251, Rennes, 2 Institut des Sciences Chimiques de Rennes, Ecole Nationale Supérieure de Chimie de Rennes, UMR CNRS 6226, Rennes, 3 Laboratoire Ondes et Milieux Complexes, UMR CNRS 6294, Le

Havre

The molecular diversity of the cold interstellar medium has been recently enriched with the detection of anions. Despite growing interest, the physical and chemical processes that govern their abundance remain poorly known. A better knowledge of anion reactivity, including chemical kinetics and branching ratios between exit channels at the relevant, low temperature of the interstellar medium, is of crucial importance for properly modelling gaseous cold environments.

To address these questions, we have conducted a series of experiments using the CRESU (French acronym standing for Kinetics of Reactions in Uniform Supersonic Flows) combined with quadrupole mass spectrometry to explore the reactivity of a selection of molecular anions down to 50 K. In our setup, the anions are produced by electron dissociative attachment on a specific precursor directly in the supersonic flow with the help of an electron gun.

The mode of production of the ions employed under this configuration is however limited to the species, such as CxN― (x = 1, 3, 5), whose precursors easily attach low energy electrons and are available or synthesizable. In order to overcome these limitations, we have developed another methodology that relies on the implementation of a mass-‐selective source of ions on the CRESU chamber. The objective is to extend our study to the reactivity of the ions of the Cx― and CxH― families, some of which have been identified in the interstellar medium: C4H―, C6H― and C8H―. Preliminary results with this new set-‐up will be presented.

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Kinetics of metastable states and atoms in DC discharges in pure O2: an experimental study

J.P.Booth1, A.Chatterjee1,2, O.Guaitella1, N.de Oliveira2, L.Nahon2, C.Western3, S.Zyryanov4 and

D.Lopaev4 1 Laboratoire de Physique des Plasmas, CNRS, Ecole Polytechnique, UPMC Univ Paris 06, Univ Paris-Sud, Observatoire de Paris,Université Paris-Saclay, Sorbonne Universités, PSL Research University, F-91128 Palaiseau, France 2 Synchrotron Soleil, 91192 Gif-sur-Yvette, France 3 School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, UK 4 Faculty of Physics, Lomonosov State University, Russian Federation

A comprehensive study of DC discharges in pure O2 gas in a Pyrex tube is presented using a range of diagnostics. Fourier-transform vacuum ultraviolet absorption spectroscopy (FT-VUVAS) provided high-resolution (106) spectra in the region 120-170 nm of O2 (X), O2 (a), O2 (b) and ground state O atoms, allowing their absolute densities to be determined. Optical Emission Spectroscopy (OAS) was used to determine the gas temperature from the O2 (b→X) emission spectrum. Time-resolved OAS of partially-modulated discharges was used to probe the loss rates of O2 (b) and of O atoms. From these measurements the surface loss coefficients of these species can be determined, as well as the rate constants for electron impact dissociation of O2. A remarkable increase in the surface loss coefficient on Pyrex of O2 (b) and O atoms is observed at low pressures, corresponding to the onset of energetic ion bombardment.

Acetone decomposition kinetics in plasmas of N2/O2 mixtures

N. Blin-Simiand*, B. Bournonville, L. Magne, S. Pasquiers LPGP, Univ. Paris-Sud, CNRS (UMR 8578), Univ. Paris-Saclay

(*) corresponding author: [email protected]

1 Experiments and kinetic models The kinetics of acetone is studied in transient homogeneous (photo-trigerred discharge, UV510 device [1]) and filamentary (dielectric barrier discharge – DBD – DC-pulsed, rod-cylinder type [2]) plasmas of N2/O2 mixtures at a pressure of 460 mbar and 1 bar respectively (ambient temperature), for molecule concentration ranging from 200 up to 5500 ppm. For the UV510, experimental data can be compared to predictions of a self-consistent modeling coupling the discharge physics to the plasma chemistry and new kinetic data can be proposed without making restrictive assumption about the electrical energy deposition into the discharge. For the DBD-reactor, a comprehensive kinetic interpretation of measurements is quite difficult because it requires a self-consistent modeling of both the streamer physics and the chemistry of the gas mixture. Therefore a simplified modeling, non self-consistent, was developed [3].

2 Results for nitrogen plasmas Below is shown an example of removed acetone concentration in the discharge of the UV510 device.

Removed concentration in the UV510-reactor for input acetone concentrations ranging from 200 up to 5500 ppm in N2. Lines: predictions of a self-consistent 0D model coupling electrical energy deposition and plasma kinetics. Quenching coefficient k (A3Σ+

u) = 1.1x 10-10 cm3s-1.

Line A in Fig.1 corresponds to the following quenching of N2 metastable states:

N2(A3Σ+u) + CH3COCH3 → H + CH3COCH2 + N2 (1)

whereas for B:

N2(A3Σ+u) + CH3COCH3 → CH3 + CH3CO + N2 (2)

and for C both (1) and (2) with same branching ratios (Same processes for the group of singlets a' 1Σ-u,

a 1Πg, and w 1Δu).

Prospects These results emphasize the critical role of N2 states quenching collisions and of radical kinetics, H and CH3, to be more studied in the future. Effect of oxygen addition to the mixture will be also analyzed.

References [1] L. Magne et al., J. Phys. D : Appl. Phys., 40 (2007) 3112-3127. [2] N. Blin-Simiand et al., 23rd ESCAMPIG, Bratisalava, Slovaquie (12-16 juillet 2016). Proceedings, 297-298. [3] S. Pasquiers et al., Eur. Phys. J.: Appl. Phys., 75 (2016) 24703 (8pp).

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Abhyuday Chatterjee LPP (Ecole Polytechnique) [email protected] Von Keudell Ruhr-Universität Bochum [email protected] Lopes LCP (Université Paris-Sud) [email protected] Chatain LATMOS (Institut Pierre Simon Laplace) [email protected] Liu LPP (Ecole Polytechnique) [email protected] Mitchell SPM (Université Rennes 1) [email protected] Alcaraz LCP (Université Paris-Sud) [email protected] Romanzin LCP (Université Paris-Sud) [email protected] Crépin ISMO (Université Paris-Sud) [email protected] Ascenzi Dept. of Physics (University of Trento) [email protected] Magdalena Staicu Casagrande ISMO (Université Paris-Sud) [email protected] Esposito IMIP (CNR Bari) [email protected] Maynard LPGP (Université Paris-Sud) [email protected] Garcia SYNCHROTRON SOLEIL [email protected]élène Mestdagh LCP (Université Paris-Sud) [email protected] Hrodmarsson SYNCHROTRON SOLEIL [email protected] Orel LCPMR (UPMC) [email protected] Schneider LOMC (Université du Havre) [email protected] Arancibia Monreal LPP (Ecole Polytechnique) [email protected] Loison ISM (Université de Bordeaux) [email protected] Booth LPP (Ecole Polytechnique) [email protected] Gorfinkiel School of Physical Sciences (Open University) [email protected]ël Lemaire LCP (Université Paris-Sud) [email protected] Van Der Beek LSI (Ecole Polytechnique) [email protected] Ito SYNCHROTRON SOLEIL [email protected] Nahon SYNCHROTRON SOLEIL [email protected] Magne LPGP (Université Paris-Sud) [email protected] Biennier SPM (Université Rennes 1) [email protected] Carrasco LATMOS (Institut Pierre Simon Laplace) [email protected] De Oliveira SYNCHROTRON SOLEIL [email protected] Sisourat LCPMR (UPMC) [email protected] Blin Simiand LCPMR (UPMC) [email protected] Pernot LCP (Université Paris-Sud) [email protected] Viegas LPP (Ecole Polytechnique) [email protected] Archirel LCP (Université Paris-Sud) [email protected] Mariotto EM2C (Centrale Paris) [email protected] Thissen LCP (Université Paris-Sud) [email protected]éphane Pasquiers LPGP (Université Paris-Sud) [email protected] Starikovskaia LPP (Ecole Polytechnique) [email protected]

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Workshop REACPLASJean-Christophe Loison (ISM, CNRS - Univ. Bordeaux I, Bordeaux, France) 17:10 –...

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Transcript of Workshop REACPLASJean-Christophe Loison (ISM, CNRS - Univ. Bordeaux I, Bordeaux, France) 17:10 –...