Nanosecond pulsed discharge plasma shows a high degree of non-equilibrium, and exhibits relativel... more Nanosecond pulsed discharge plasma shows a high degree of non-equilibrium, and exhibits relatively high conversions in the dry reforming of methane. To further improve the application, a good insight of the underlying mechanisms is desired. We developed a chemical kinetics model to explore the underlying plasma chemistry in nanosecond pulsed discharge. We compared the calculated conversions and product selectivities with experimental results, and found reasonable agreement in a wide range of specific energy input. Hence, the chemical kinetics model is able to provide insight in the underlying plasma chemistry. The modeling results predict that the most important dissociation reaction of CO2 and CH4 is electron impact dissociation. C2H2 is the most abundant hydrocarbon product, and it is mainly formed upon reaction of two CH2 radicals. Furthermore, the vibrational excitation levels of CO2 contribute for 85% to the total dissociation of CO2.
Over the years, until the present days, a persistent mistake has been found in the literature: th... more Over the years, until the present days, a persistent mistake has been found in the literature: the use of the ‘vibrational temperature’ of an emitting electronic state as somewhat representative of the vibrational temperature of the gas in the discharge. Such a temperature is determined by fitting the spectra measured by optical emission spectroscopy. Besides the misuse of the word temperature, the results of such fittings are ambiguously named ‘vibrational temperature’ and sometimes used to argue about the vibrational non-equilibrium and its variation with discharge conditions. What has this temperature to do with the vibrational excitation of the molecules’ ground state, i.e. of the large majority of gas components? It is well established that the connection between the vibrational population of the excited and the ground state exists through the excitation process, the collisional quenching, and the vibrational relaxation in the manifold of the excited state. Nevertheless, this i...
<p><strong>Introduction:</strong&g... more <p><strong>Introduction:</strong></p> <p>Charged species have been detected at various stages of stellar evolution, from pre- and protostellar objects to planet-forming disks, where they can be used as signatures of the build-up in chemical complexity [1, 2, 3, 4, 5]. On the other hand, on planets and planetary bodies with atmospheres exposed to photons and energetic particles, ionic reactions have been suggested as playing a significant role in the build-up of chemical complexity. A good example is the atmosphere of Titan, where the CASSINI mission [6] detected, by mass spectrometry, a wide range of N-containing organic ions, and photochemical models [7, 8] predict that these ions trigger a rich gas-phase chemistry, eventually forming tholins, a key ingredient of Titan’s haze [9]. Similar effects may be expected in the atmospheres of exoplanets, for which simulation experiments indicate that complex photochemistry can take place leading to formation of large molecules [10, 11]. It has been suggested that complex organic molecules (COMs) could be synthesised through reactions on dust grains, a process which might be facilitated by the acceleration of cations in the gas phase towards negatively charged dust grains [12]. It is therefore important to understand the gas-phase ion chemistry of these environments in order to develop reliable chemical models.</p> <p> </p> <p><strong>Results:</strong></p> <p>In our laboratories, we measure kinetic parameters (cross sections, branching ratios and their dependences on collision energy) for the reaction of charged molecules with neutrals, using tandem mass spectrometric techniques and RF octupolar trapping of parent and product ions.</p> <p>In this contribution, we examine the reactions of two isomers of [CNH<sub>3</sub>]<sup>+</sup> that are believed to contribute to the m/z 29 peak observed in the aforementioned mass spectra of Titan’s atmosphere, namely HCNH<sub>2</sub><sup>+</sup> and H<sub>2</sub>CNH<sup>+</sup>, with a range of neutrals including both saturated; CH<sub>4</sub>; and unsaturated; C<sub>2</sub>H<sub>2</sub>, C<sub>2</sub>H<sub>4</sub>, C<sub>3</sub>H<sub>4</sub> (allene), C<sub>3</sub>H<sub>4</sub> (propyne) and C<sub>3</sub>H<sub>6</sub>; hydrocarbons as well as some simple nitriles; CH<sub>3</sub>CN and C<sub>2</sub>H<sub>3</sub>CN; and CH<sub>3</sub>OH with the objective of identifying the reaction pathways present as well as their respective rate constants and branching ratios.</p> <p><strong> </strong></p> <p><strong>Experimental Methods: </strong>The data presented here for the HCNH<sub>2</sub><sup>+</sup> and H<sub>2</sub>CNH<sup>+</sup> ions were collected using the CERISES instrument attached to the DESIRS beamline of the French SOLEIL synchrotron [13], using VUV photons to generate ions through either direct photoionization or dissociative photoionization of suitable neutral precursors. The HCNH<sub>2</sub><sup>+</sup> ion was generated exclusively through dissociative photoionization of cyclopropylamine (C<sub>3</sub>H<sub>7</sub>N)[14] while H<sub>2</sub>CNH<sup>+</sup> was generated both through dissociative photoionization of azetidine (C<sub>3</sub>H<sub>7</sub>N also) and via direct photoionization of neutral methanimine, produced via a gas-solid reaction between aminoacetonitrile in gas phase and powdered potassium hydroxide [15]. Working in this way allows us to present data as a function of the energy of the photons used in the ionisation; which in the case of direct ionisation is a proxy for the internal energy of the ions; as well as as a function of the collision energy. Ab initio calculations have also been performed for some of these reactions, with…
Chemphyschem : a European journal of chemical physics and physical chemistry, Jan 18, 2017
Long-range intermolecular forces play a crucial role in controlling the outcome of ion-molecule c... more Long-range intermolecular forces play a crucial role in controlling the outcome of ion-molecule chemical reactions, such as those determining the disappearance of organic or inorganic "complex" molecules recently detected in various regions of the interstellar medium due to collisions with abundant interstellar atomic ions (e.g. H+ and He+ ). Theoretical treatments, for example, based on simple capture models, are nowadays often adopted to evaluate the collision-energy dependence of reactive cross sections and the temperature dependent rate coefficients of many ion-molecule reactions. The obtained results are widely used for the modelling of phenomena occurring in different natural environments or technological applications such as astrophysical and laboratory plasmas. Herein it is demonstrated, through a combined experimental and theoretical investigation on a prototype ion-molecule reaction (He+ +methyl formate), that the dynamics, investigated in detail, shows some intr...
Plasma Sources Science and Technology, Dec 1, 2008
We have investigated CN(B (2)Sigma(+) - X (2)Sigma(+)) violet system emission and laser induced f... more We have investigated CN(B (2)Sigma(+) - X (2)Sigma(+)) violet system emission and laser induced fluorescence in an atmospheric pressure pulsed dielectric barrier discharge and found a high degree of vibrational non-equilibrium in both CN(B, v) and CN(X, v'). The vibrational distributions depend strongly on the gas feed composition and on the discharge/post-discharge regime. Analysis of the time resolved laser and
Context. To correctly model the abundances of interstellar complex organic molecules (iCOMs) in d... more Context. To correctly model the abundances of interstellar complex organic molecules (iCOMs) in different environments, both formation and destruction routes should be appropriately accounted for. While several scenarios have been explored for the formation of iCOMs via grain and gas-phase processes, much less work has been devoted to understanding the relevant destruction pathways, with special reference to (dissociative) charge exchange or proton transfer reactions with abundant atomic and molecular ions such as He+, H3+ and HCO+. Aims. By using a combined experimental and theoretical methodology we provide new values for the rate coefficients and branching ratios (BRs) of the reactions of He+ ions with two important iCOMs, namely dimethyl ether (DME) and methyl formate (MF). We also review the destruction routes of DME and MF by other two abundant ions, namely H3+ and HCO+. Methods. Based on our recent laboratory measurements of cross sections and BRs for the DME/MF + He+ reactio...
Laser induced fluorescence is intensively used for the detection of OH in many atmospheric pressu... more Laser induced fluorescence is intensively used for the detection of OH in many atmospheric pressure discharge devices. At this pressure, a quantitative knowledge of the collision phenomena in the upper excited state is critical. Here we report the measurement at T = 300 K of a set of rate constants of electronic quenching and vibrational relaxation of the OH electronic state, by collision with N2, O2, H2O, CO2, CO, H2, D2, CH4, C2H2, C2H4, C2H6. These are the main gases in applications like plasma medicine, hydrocarbons reforming and CO2 conversion. Available literature data are revisited, and new data are added, mostly relevant to quenching and vibrational relaxation.
Nanosecond pulsed discharge plasma shows a high degree of non-equilibrium, and exhibits relativel... more Nanosecond pulsed discharge plasma shows a high degree of non-equilibrium, and exhibits relatively high conversions in the dry reforming of methane. To further improve the application, a good insight of the underlying mechanisms is desired. We developed a chemical kinetics model to explore the underlying plasma chemistry in nanosecond pulsed discharge. We compared the calculated conversions and product selectivities with experimental results, and found reasonable agreement in a wide range of specific energy input. Hence, the chemical kinetics model is able to provide insight in the underlying plasma chemistry. The modeling results predict that the most important dissociation reaction of CO2 and CH4 is electron impact dissociation. C2H2 is the most abundant hydrocarbon product, and it is mainly formed upon reaction of two CH2 radicals. Furthermore, the vibrational excitation levels of CO2 contribute for 85% to the total dissociation of CO2.
Over the years, until the present days, a persistent mistake has been found in the literature: th... more Over the years, until the present days, a persistent mistake has been found in the literature: the use of the ‘vibrational temperature’ of an emitting electronic state as somewhat representative of the vibrational temperature of the gas in the discharge. Such a temperature is determined by fitting the spectra measured by optical emission spectroscopy. Besides the misuse of the word temperature, the results of such fittings are ambiguously named ‘vibrational temperature’ and sometimes used to argue about the vibrational non-equilibrium and its variation with discharge conditions. What has this temperature to do with the vibrational excitation of the molecules’ ground state, i.e. of the large majority of gas components? It is well established that the connection between the vibrational population of the excited and the ground state exists through the excitation process, the collisional quenching, and the vibrational relaxation in the manifold of the excited state. Nevertheless, this i...
<p><strong>Introduction:</strong&g... more <p><strong>Introduction:</strong></p> <p>Charged species have been detected at various stages of stellar evolution, from pre- and protostellar objects to planet-forming disks, where they can be used as signatures of the build-up in chemical complexity [1, 2, 3, 4, 5]. On the other hand, on planets and planetary bodies with atmospheres exposed to photons and energetic particles, ionic reactions have been suggested as playing a significant role in the build-up of chemical complexity. A good example is the atmosphere of Titan, where the CASSINI mission [6] detected, by mass spectrometry, a wide range of N-containing organic ions, and photochemical models [7, 8] predict that these ions trigger a rich gas-phase chemistry, eventually forming tholins, a key ingredient of Titan’s haze [9]. Similar effects may be expected in the atmospheres of exoplanets, for which simulation experiments indicate that complex photochemistry can take place leading to formation of large molecules [10, 11]. It has been suggested that complex organic molecules (COMs) could be synthesised through reactions on dust grains, a process which might be facilitated by the acceleration of cations in the gas phase towards negatively charged dust grains [12]. It is therefore important to understand the gas-phase ion chemistry of these environments in order to develop reliable chemical models.</p> <p> </p> <p><strong>Results:</strong></p> <p>In our laboratories, we measure kinetic parameters (cross sections, branching ratios and their dependences on collision energy) for the reaction of charged molecules with neutrals, using tandem mass spectrometric techniques and RF octupolar trapping of parent and product ions.</p> <p>In this contribution, we examine the reactions of two isomers of [CNH<sub>3</sub>]<sup>+</sup> that are believed to contribute to the m/z 29 peak observed in the aforementioned mass spectra of Titan’s atmosphere, namely HCNH<sub>2</sub><sup>+</sup> and H<sub>2</sub>CNH<sup>+</sup>, with a range of neutrals including both saturated; CH<sub>4</sub>; and unsaturated; C<sub>2</sub>H<sub>2</sub>, C<sub>2</sub>H<sub>4</sub>, C<sub>3</sub>H<sub>4</sub> (allene), C<sub>3</sub>H<sub>4</sub> (propyne) and C<sub>3</sub>H<sub>6</sub>; hydrocarbons as well as some simple nitriles; CH<sub>3</sub>CN and C<sub>2</sub>H<sub>3</sub>CN; and CH<sub>3</sub>OH with the objective of identifying the reaction pathways present as well as their respective rate constants and branching ratios.</p> <p><strong> </strong></p> <p><strong>Experimental Methods: </strong>The data presented here for the HCNH<sub>2</sub><sup>+</sup> and H<sub>2</sub>CNH<sup>+</sup> ions were collected using the CERISES instrument attached to the DESIRS beamline of the French SOLEIL synchrotron [13], using VUV photons to generate ions through either direct photoionization or dissociative photoionization of suitable neutral precursors. The HCNH<sub>2</sub><sup>+</sup> ion was generated exclusively through dissociative photoionization of cyclopropylamine (C<sub>3</sub>H<sub>7</sub>N)[14] while H<sub>2</sub>CNH<sup>+</sup> was generated both through dissociative photoionization of azetidine (C<sub>3</sub>H<sub>7</sub>N also) and via direct photoionization of neutral methanimine, produced via a gas-solid reaction between aminoacetonitrile in gas phase and powdered potassium hydroxide [15]. Working in this way allows us to present data as a function of the energy of the photons used in the ionisation; which in the case of direct ionisation is a proxy for the internal energy of the ions; as well as as a function of the collision energy. Ab initio calculations have also been performed for some of these reactions, with…
Chemphyschem : a European journal of chemical physics and physical chemistry, Jan 18, 2017
Long-range intermolecular forces play a crucial role in controlling the outcome of ion-molecule c... more Long-range intermolecular forces play a crucial role in controlling the outcome of ion-molecule chemical reactions, such as those determining the disappearance of organic or inorganic "complex" molecules recently detected in various regions of the interstellar medium due to collisions with abundant interstellar atomic ions (e.g. H+ and He+ ). Theoretical treatments, for example, based on simple capture models, are nowadays often adopted to evaluate the collision-energy dependence of reactive cross sections and the temperature dependent rate coefficients of many ion-molecule reactions. The obtained results are widely used for the modelling of phenomena occurring in different natural environments or technological applications such as astrophysical and laboratory plasmas. Herein it is demonstrated, through a combined experimental and theoretical investigation on a prototype ion-molecule reaction (He+ +methyl formate), that the dynamics, investigated in detail, shows some intr...
Plasma Sources Science and Technology, Dec 1, 2008
We have investigated CN(B (2)Sigma(+) - X (2)Sigma(+)) violet system emission and laser induced f... more We have investigated CN(B (2)Sigma(+) - X (2)Sigma(+)) violet system emission and laser induced fluorescence in an atmospheric pressure pulsed dielectric barrier discharge and found a high degree of vibrational non-equilibrium in both CN(B, v) and CN(X, v'). The vibrational distributions depend strongly on the gas feed composition and on the discharge/post-discharge regime. Analysis of the time resolved laser and
Context. To correctly model the abundances of interstellar complex organic molecules (iCOMs) in d... more Context. To correctly model the abundances of interstellar complex organic molecules (iCOMs) in different environments, both formation and destruction routes should be appropriately accounted for. While several scenarios have been explored for the formation of iCOMs via grain and gas-phase processes, much less work has been devoted to understanding the relevant destruction pathways, with special reference to (dissociative) charge exchange or proton transfer reactions with abundant atomic and molecular ions such as He+, H3+ and HCO+. Aims. By using a combined experimental and theoretical methodology we provide new values for the rate coefficients and branching ratios (BRs) of the reactions of He+ ions with two important iCOMs, namely dimethyl ether (DME) and methyl formate (MF). We also review the destruction routes of DME and MF by other two abundant ions, namely H3+ and HCO+. Methods. Based on our recent laboratory measurements of cross sections and BRs for the DME/MF + He+ reactio...
Laser induced fluorescence is intensively used for the detection of OH in many atmospheric pressu... more Laser induced fluorescence is intensively used for the detection of OH in many atmospheric pressure discharge devices. At this pressure, a quantitative knowledge of the collision phenomena in the upper excited state is critical. Here we report the measurement at T = 300 K of a set of rate constants of electronic quenching and vibrational relaxation of the OH electronic state, by collision with N2, O2, H2O, CO2, CO, H2, D2, CH4, C2H2, C2H4, C2H6. These are the main gases in applications like plasma medicine, hydrocarbons reforming and CO2 conversion. Available literature data are revisited, and new data are added, mostly relevant to quenching and vibrational relaxation.
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Papers by Paolo Tosi