A. Bergeat | Université de Bordeaux (original) (raw)
Papers by A. Bergeat
IAU …, 2005
Abstract. CH radical reactions with hydrocarbons could play a role in the atmospheres of Titan, P... more Abstract. CH radical reactions with hydrocarbons could play a role in the atmospheres of Titan, Pluto or Triton as well as in interstellar clouds (ISCs), where the hydrocarbon compounds were detected and the temperatures are very low, ie∼ 95 K down to∼ 38 K at ...
Physical Chemistry Chemical Physics, 2004
... Nadia Balucania, Giovanni Capozzaa, Laura Cartechinia, Astrid Bergeat§a, Rolf Bobbenkamp¶a, ... more ... Nadia Balucania, Giovanni Capozzaa, Laura Cartechinia, Astrid Bergeat§a, Rolf Bobbenkamp¶a, Piergiorgio Casavecchia*a, F. Javier Aoizb, Luis Bañaresb, Pascal Honvaultc, Béatrice Bussery-Honvaultc and Jean-Michel Launayc. ...
The Journal of Physical Chemistry A, 1999
ABSTRACT
The Journal of Physical Chemistry A, 1998
ABSTRACT
Physical Chemistry Chemical Physics, 2004
ABSTRACT
The Journal of Chemical Physics, 2002
ABSTRACT The reaction between atomic carbon and acetylene has been investigated using complementa... more ABSTRACT The reaction between atomic carbon and acetylene has been investigated using complementary crossed molecular beam techniques. Differential cross sections have been obtained for the reactions of both ground and excited carbon atoms, C(3PJ, 1D2)+C2H2(X 1Σg+), in experiments conducted with continuous supersonic beams, mass spectrometric detection, and time-of-flight analysis at a relative translational energy of 29.3 kJ mol−1. The reaction C(3PJ)+C2H2(X 1Σg+) has been found to lead to C3H+H and C3+H2 products in comparable amounts. Both H and H2 elimination pathways are found to proceed through the formation of a C3H2 long-lived intermediate complex whose lifetime may be comparable to its rotational period. The spin-forbidden H2 elimination channel is attributed to the occurrence of intersystem-crossing between the triplet and singlet manifolds of the C3H2 potential-energy surfaces. The reaction C(1D2)+C2H2(X 1Σg+) has been found to lead to formation of C3H+H, with a C3H center-of-mass angular distribution strongly forward peaked, indicating a short-lived intermediate complex. Integral cross sections have been obtained for the C(3PJ)+C2H2(X 1Σg+)→C3H+H(2S1/2) reaction in experiments conducted with pulsed, supersonic molecular beams in the range of relative translational energies ET = 0.38−25.5 kJ mol−1, the H(2S1/2) product being detected by laser-induced fluorescence. The reaction has been found to be without a barrier, relative integral cross sections being proportional to (ET)−0.80±0.03 below ET = 10 kJ mol−1. These findings provide direct evidence that the C(3PJ)+C2H2 reaction can occur under the physical conditions prevailing in dense interstellar clouds and, in particular, that it may be the source of both C3H and C3 species in these extreme environments. © 2002 American Institute of Physics.
Faraday Discussions, 2001
The dynamics of some elementary reactions of N(2D), C(3P,1D) and CN(X2 sigma +) of importance in ... more The dynamics of some elementary reactions of N(2D), C(3P,1D) and CN(X2 sigma +) of importance in combustion have been investigated by using the crossed molecular beam scattering method with mass spectrometric detection. The novel capability of producing intense, continuous beams of the radical reagents by a radio-frequency discharge beam source was exploited. From angular and velocity distribution measurements obtained in the laboratory frame, primary reaction products have been identified and their angular and translational energy distributions in the center-of-mass system, as well as branching ratios, have been derived. The dominant N/H exchange channel has been examined in the reaction N(2D) + CH4, which is found to lead to H + CH2NH (methylenimine) and H + CH3N (methylnitrene); no H2 elimination is observed. In the reaction N(2D) + H2O the N/H exchange channel has been found to occur via two competing pathways leading to HNO + H and HON + H, while formation of NO + H2 is negligible. Formation of H + H2CCCH (propargyl) is the dominant pathway, at low collision energy (Ec), of the C(3P) + C2H4 reaction, while at high Ec formation of the less stable C3H3 isomers (cyclopropenyl and/or propyn-1-yl) also occurs; the H2 elimination channel is negligible. The H elimination channel has also been found to be the dominant pathway in the C(3P,1D) + CH3CCH reaction leading to C4H3 isomers and, again, no H2 elimination has been observed to occur. In contrast, both H and H2 elimination, leading in comparable ratio to C3H + H and C3(X1 sigma g+) + H2(X1 sigma g+), respectively, have been observed in the reaction C(3P) + C2H2(X1 sigma g+). The occurrence of the spin-forbidden molecular pathway in this reaction, never detected before, has been rationalized by invoking the occurrence of intersystem crossing between triplet and singlet manifolds of the C3H2 potential energy surfaces. The reaction CN(X2 sigma +) + C2H2 has been found to lead to internally excited HCCCN (cyanoacetylene) + H. For all the reactions the dynamics have been discussed in the light of recent theoretical calculations on the relevant potential energy surfaces. Previous, lower resolution studies on C and CN reactions carried out using pulsed beams are noted. Finally, throughout the paper the relevance of these results to combustion chemistry is considered.
Faraday Discussions, 2001
The multichannel CH + O2 reaction was studied at room temperature, in a low-pressure fast-flow re... more The multichannel CH + O2 reaction was studied at room temperature, in a low-pressure fast-flow reactor. CH radical was obtained from the reaction of CHBr3 with potassium atoms. The overall rate constant was determined from the decay of CH with distance, O2 being introduced in excess. The result, after corrections for axial and radial diffusion, is k = (3.6 +/- 0.5) x 10(-11) cm3 molecule-1 s-1. The OH(A2 sigma +) chemiluminescence was observed, confirming the existence of the OH + CO channel. The vibrational population distribution of OH(A2 sigma +) is 32% in the v' = 1 level and 68% in the v' = 0 level (+/- 5%). The relative atomic concentrations were determined by resonance fluorescence in the vacuum ultraviolet. A ratio of 1.4 +/- 0.2 was found between the H atom density (H atoms being produced from the H + CO2 channel and from the HCO dissociation) and the O atom density (O + HCO). Ab initio calculations of the transition structures have been performed, associated with statistical estimations. The estimated branching ratios are: O + HCO, 20%; O + H + CO, 30%; H + CO2, 30%; and CO + OH, 20%.
Chemical Physics Letters, 1999
The C q NO and C q O reactions were studied, at room temperature, in a low-pressure fast-flow rea... more The C q NO and C q O reactions were studied, at room temperature, in a low-pressure fast-flow reactor. C atoms were 2 obtained from the reaction of CBr or CCl with potassium atoms and probed by their VUV resonance fluorescence. For 4 4 0009-2614r99r$ -see front matter q 1999 Elsevier Science B.V. All rights reserved. Ž . PII: S 0 0 0 9 -2 6 1 4 9 9 0 0 5 8 6 -2 ( ) A. Bergeat et al.r Chemical Physics Letters 308 1999 7-12 8
Chemical Physics Letters, 2000
The reaction of potassium atoms with C NCl , CCl , and C Cl have been used to produce C N, CCl, a... more The reaction of potassium atoms with C NCl , CCl , and C Cl have been used to produce C N, CCl, and C radicals.
Chemical Physics Letters, 2000
Product angular and time-of-flight distributions have been measured for the first time for the pr... more Product angular and time-of-flight distributions have been measured for the first time for the prototypical insertion reaction C(1D)+H2 using the crossed-beam technique with mass spectrometric detection at the collision energy of 1.86 kcal mol−1. Center-of-mass angular and kinetic energy distributions have been derived for CH(X2Π, v′=0)+H products and compared with those of statistical calculations based on phase-space theory.
Chemical Physics, 1997
C 2 radicals were prepared from the overall reaction 4K + C2C14 --> 4KC1 + C 2 and mixed with ato... more C 2 radicals were prepared from the overall reaction 4K + C2C14 --> 4KC1 + C 2 and mixed with atomic nitrogen in a low-pressure fast-flow reactor. CN(X 2~ +) produced by the exoergic reaction N + C 2 ~ CN + C was probed by laser-induced fluorescence. Vibrational distributions at different distances from the reactant mixing zone were determined. Fitting of the evolution of the vibrational distribution, using a kinetic scheme which included the collisional transfer between X 2 ~ + and A2[Ii vibrational levels and CN removal by the N + CN ~ C + N 2 reaction, allowed to determine the nascent vibrational distribution given by the N + C 2 reaction. This distribution was found to be non-statistical and is compared to that obtained from the C + NO ~ CN + O reaction in a previous crossed-beam study.
Astronomy & Astrophysics, 2013
Astronomy & Astrophysics, 2012
The reactions of excited nitrogen atoms, N(2D), with methane, ethene and ethyne, have been studie... more The reactions of excited nitrogen atoms, N(2D), with methane, ethene and ethyne, have been studied under single collision conditions in order to identify possible reaction products. In all cases, the nitrogen/hydrogen exchange channel was found to be a significant reaction pathway, leading to nitrogen containing molecules or radicals. The present laboratory studies are helpful in modeling the chemistry of the upper atmosphere of Titan, since they confirm that reactions of N(2D) are effective in generating new C-N bonds and therefore represent potential first steps towards the formation of nitriles. Relevant to the organic chemistry of Titan atmosphere are the following finds: 1) CH2NH is the main reaction product from the reaction N(2D)+CH4; 2) the products of formula C2H3N generated by the N(2D)+C2H4 reaction are formed with enough internal energy to easily rearrange to the most stable isomer CH3CN; 3) the main product from N(2D)+C2H2 reaction is HCCN. We recall that both CH2NH and CH3CN have been observed in the atmosphere of Titan, while the HCCN radical has been suggested to be a key intermediate towards C2N2/C2N4 formation.
EAS Publications Series, 2012
IAU …, 2005
Abstract. CH radical reactions with hydrocarbons could play a role in the atmospheres of Titan, P... more Abstract. CH radical reactions with hydrocarbons could play a role in the atmospheres of Titan, Pluto or Triton as well as in interstellar clouds (ISCs), where the hydrocarbon compounds were detected and the temperatures are very low, ie∼ 95 K down to∼ 38 K at ...
Physical Chemistry Chemical Physics, 2004
... Nadia Balucania, Giovanni Capozzaa, Laura Cartechinia, Astrid Bergeat§a, Rolf Bobbenkamp¶a, ... more ... Nadia Balucania, Giovanni Capozzaa, Laura Cartechinia, Astrid Bergeat§a, Rolf Bobbenkamp¶a, Piergiorgio Casavecchia*a, F. Javier Aoizb, Luis Bañaresb, Pascal Honvaultc, Béatrice Bussery-Honvaultc and Jean-Michel Launayc. ...
The Journal of Physical Chemistry A, 1999
ABSTRACT
The Journal of Physical Chemistry A, 1998
ABSTRACT
Physical Chemistry Chemical Physics, 2004
ABSTRACT
The Journal of Chemical Physics, 2002
ABSTRACT The reaction between atomic carbon and acetylene has been investigated using complementa... more ABSTRACT The reaction between atomic carbon and acetylene has been investigated using complementary crossed molecular beam techniques. Differential cross sections have been obtained for the reactions of both ground and excited carbon atoms, C(3PJ, 1D2)+C2H2(X 1Σg+), in experiments conducted with continuous supersonic beams, mass spectrometric detection, and time-of-flight analysis at a relative translational energy of 29.3 kJ mol−1. The reaction C(3PJ)+C2H2(X 1Σg+) has been found to lead to C3H+H and C3+H2 products in comparable amounts. Both H and H2 elimination pathways are found to proceed through the formation of a C3H2 long-lived intermediate complex whose lifetime may be comparable to its rotational period. The spin-forbidden H2 elimination channel is attributed to the occurrence of intersystem-crossing between the triplet and singlet manifolds of the C3H2 potential-energy surfaces. The reaction C(1D2)+C2H2(X 1Σg+) has been found to lead to formation of C3H+H, with a C3H center-of-mass angular distribution strongly forward peaked, indicating a short-lived intermediate complex. Integral cross sections have been obtained for the C(3PJ)+C2H2(X 1Σg+)→C3H+H(2S1/2) reaction in experiments conducted with pulsed, supersonic molecular beams in the range of relative translational energies ET = 0.38−25.5 kJ mol−1, the H(2S1/2) product being detected by laser-induced fluorescence. The reaction has been found to be without a barrier, relative integral cross sections being proportional to (ET)−0.80±0.03 below ET = 10 kJ mol−1. These findings provide direct evidence that the C(3PJ)+C2H2 reaction can occur under the physical conditions prevailing in dense interstellar clouds and, in particular, that it may be the source of both C3H and C3 species in these extreme environments. © 2002 American Institute of Physics.
Faraday Discussions, 2001
The dynamics of some elementary reactions of N(2D), C(3P,1D) and CN(X2 sigma +) of importance in ... more The dynamics of some elementary reactions of N(2D), C(3P,1D) and CN(X2 sigma +) of importance in combustion have been investigated by using the crossed molecular beam scattering method with mass spectrometric detection. The novel capability of producing intense, continuous beams of the radical reagents by a radio-frequency discharge beam source was exploited. From angular and velocity distribution measurements obtained in the laboratory frame, primary reaction products have been identified and their angular and translational energy distributions in the center-of-mass system, as well as branching ratios, have been derived. The dominant N/H exchange channel has been examined in the reaction N(2D) + CH4, which is found to lead to H + CH2NH (methylenimine) and H + CH3N (methylnitrene); no H2 elimination is observed. In the reaction N(2D) + H2O the N/H exchange channel has been found to occur via two competing pathways leading to HNO + H and HON + H, while formation of NO + H2 is negligible. Formation of H + H2CCCH (propargyl) is the dominant pathway, at low collision energy (Ec), of the C(3P) + C2H4 reaction, while at high Ec formation of the less stable C3H3 isomers (cyclopropenyl and/or propyn-1-yl) also occurs; the H2 elimination channel is negligible. The H elimination channel has also been found to be the dominant pathway in the C(3P,1D) + CH3CCH reaction leading to C4H3 isomers and, again, no H2 elimination has been observed to occur. In contrast, both H and H2 elimination, leading in comparable ratio to C3H + H and C3(X1 sigma g+) + H2(X1 sigma g+), respectively, have been observed in the reaction C(3P) + C2H2(X1 sigma g+). The occurrence of the spin-forbidden molecular pathway in this reaction, never detected before, has been rationalized by invoking the occurrence of intersystem crossing between triplet and singlet manifolds of the C3H2 potential energy surfaces. The reaction CN(X2 sigma +) + C2H2 has been found to lead to internally excited HCCCN (cyanoacetylene) + H. For all the reactions the dynamics have been discussed in the light of recent theoretical calculations on the relevant potential energy surfaces. Previous, lower resolution studies on C and CN reactions carried out using pulsed beams are noted. Finally, throughout the paper the relevance of these results to combustion chemistry is considered.
Faraday Discussions, 2001
The multichannel CH + O2 reaction was studied at room temperature, in a low-pressure fast-flow re... more The multichannel CH + O2 reaction was studied at room temperature, in a low-pressure fast-flow reactor. CH radical was obtained from the reaction of CHBr3 with potassium atoms. The overall rate constant was determined from the decay of CH with distance, O2 being introduced in excess. The result, after corrections for axial and radial diffusion, is k = (3.6 +/- 0.5) x 10(-11) cm3 molecule-1 s-1. The OH(A2 sigma +) chemiluminescence was observed, confirming the existence of the OH + CO channel. The vibrational population distribution of OH(A2 sigma +) is 32% in the v' = 1 level and 68% in the v' = 0 level (+/- 5%). The relative atomic concentrations were determined by resonance fluorescence in the vacuum ultraviolet. A ratio of 1.4 +/- 0.2 was found between the H atom density (H atoms being produced from the H + CO2 channel and from the HCO dissociation) and the O atom density (O + HCO). Ab initio calculations of the transition structures have been performed, associated with statistical estimations. The estimated branching ratios are: O + HCO, 20%; O + H + CO, 30%; H + CO2, 30%; and CO + OH, 20%.
Chemical Physics Letters, 1999
The C q NO and C q O reactions were studied, at room temperature, in a low-pressure fast-flow rea... more The C q NO and C q O reactions were studied, at room temperature, in a low-pressure fast-flow reactor. C atoms were 2 obtained from the reaction of CBr or CCl with potassium atoms and probed by their VUV resonance fluorescence. For 4 4 0009-2614r99r$ -see front matter q 1999 Elsevier Science B.V. All rights reserved. Ž . PII: S 0 0 0 9 -2 6 1 4 9 9 0 0 5 8 6 -2 ( ) A. Bergeat et al.r Chemical Physics Letters 308 1999 7-12 8
Chemical Physics Letters, 2000
The reaction of potassium atoms with C NCl , CCl , and C Cl have been used to produce C N, CCl, a... more The reaction of potassium atoms with C NCl , CCl , and C Cl have been used to produce C N, CCl, and C radicals.
Chemical Physics Letters, 2000
Product angular and time-of-flight distributions have been measured for the first time for the pr... more Product angular and time-of-flight distributions have been measured for the first time for the prototypical insertion reaction C(1D)+H2 using the crossed-beam technique with mass spectrometric detection at the collision energy of 1.86 kcal mol−1. Center-of-mass angular and kinetic energy distributions have been derived for CH(X2Π, v′=0)+H products and compared with those of statistical calculations based on phase-space theory.
Chemical Physics, 1997
C 2 radicals were prepared from the overall reaction 4K + C2C14 --> 4KC1 + C 2 and mixed with ato... more C 2 radicals were prepared from the overall reaction 4K + C2C14 --> 4KC1 + C 2 and mixed with atomic nitrogen in a low-pressure fast-flow reactor. CN(X 2~ +) produced by the exoergic reaction N + C 2 ~ CN + C was probed by laser-induced fluorescence. Vibrational distributions at different distances from the reactant mixing zone were determined. Fitting of the evolution of the vibrational distribution, using a kinetic scheme which included the collisional transfer between X 2 ~ + and A2[Ii vibrational levels and CN removal by the N + CN ~ C + N 2 reaction, allowed to determine the nascent vibrational distribution given by the N + C 2 reaction. This distribution was found to be non-statistical and is compared to that obtained from the C + NO ~ CN + O reaction in a previous crossed-beam study.
Astronomy & Astrophysics, 2013
Astronomy & Astrophysics, 2012
The reactions of excited nitrogen atoms, N(2D), with methane, ethene and ethyne, have been studie... more The reactions of excited nitrogen atoms, N(2D), with methane, ethene and ethyne, have been studied under single collision conditions in order to identify possible reaction products. In all cases, the nitrogen/hydrogen exchange channel was found to be a significant reaction pathway, leading to nitrogen containing molecules or radicals. The present laboratory studies are helpful in modeling the chemistry of the upper atmosphere of Titan, since they confirm that reactions of N(2D) are effective in generating new C-N bonds and therefore represent potential first steps towards the formation of nitriles. Relevant to the organic chemistry of Titan atmosphere are the following finds: 1) CH2NH is the main reaction product from the reaction N(2D)+CH4; 2) the products of formula C2H3N generated by the N(2D)+C2H4 reaction are formed with enough internal energy to easily rearrange to the most stable isomer CH3CN; 3) the main product from N(2D)+C2H2 reaction is HCCN. We recall that both CH2NH and CH3CN have been observed in the atmosphere of Titan, while the HCCN radical has been suggested to be a key intermediate towards C2N2/C2N4 formation.
EAS Publications Series, 2012