Combined crossed molecular beams and computational study on the N(2D) + HCCCN(X1Σ+) reaction and implications for extra-terrestrial environments

Liang, Pengxiao; Mancini, Luca; Marchione, Demian; Vanuzzo, Gianmarco; Ferlin, Francesco; Recio, Pedro; Tan, Yan Fei; Pannacci, Giacomo; Vaccaro, Luigi; Rosi, Marzio; Casavecchia, Piergiorgio; Balucani, Nadia

doi:10.1080/00268976.2021.1948126

Cited by 12 publications

(16 citation statements)

References 82 publications

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“…The first reaction we have looked at is the one involving cyanoacetylene, HCCCN. 41 We have verified that the formation of dicyanocarbene, NCCCN, is the main reaction channel, at odds with respect to what is considered in most recent models 23 where three possible product channels are instead assumed for the N( 2 D) + HCCCN reaction: (i) N 2 + c-C 3 H, (ii) N 2 + l-C 3 H, and (iii) C 2 N + HCN. Here, we extend the same combined experimental and theoretical approach to the reaction N( 2 D) + CH 2 CHCN (vinyl cyanide).…”

Section: Introductionmentioning

confidence: 62%

“…Nitriles, such as CH 3 CN, C 2 H 3 CN, C 2 H 5 CN, and HCCCN, have been observed in the atmosphere of Titan and reach a certain abundance at altitudes above 1000 km, a region where N( 2 D) is also formed by the high energy processes mentioned above. The first reaction we have looked at is the one involving cyanoacetylene, HCCCN . We have verified that the formation of dicyanocarbene, NCCCN, is the main reaction channel, at odds with respect to what is considered in most recent models where three possible product channels are instead assumed for the N( 2 D) + HCCCN reaction: (i) N 2 + c -C 3 H, (ii) N 2 + l -C 3 H, and (iii) C 2 N + HCN.…”

Section: Introductionmentioning

confidence: 71%

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The N(²D) + CH₂CHCN (Vinyl Cyanide) Reaction: A Combined Crossed Molecular Beam and Theoretical Study and Implications for the Atmosphere of Titan

et al. 2022

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The reaction of electronically excited nitrogen atoms, N( 2 D), with vinyl cyanide, CH 2 CHCN, has been investigated under single-collision conditions by the crossed molecular beam (CMB) scattering method with mass spectrometric detection and time-of-flight (TOF) analysis at the collision energy, E c , of 31.4 kJ/mol. Synergistic electronic structure calculations of the doublet potential energy surface (PES) have been performed to assist in the interpretation of the experimental results and characterize the overall reaction micromechanism. Statistical (Rice–Ramsperger–Kassel–Marcus, RRKM) calculations of product branching fractions (BFs) on the theoretical PES have been carried out at different values of temperature, including the one corresponding to the temperature (175 K) of Titan’s stratosphere and at a total energy corresponding to the E c of the CMB experiment. According to our theoretical calculations, the reaction is found to proceed via barrierless addition of N( 2 D) to the carbon–carbon double bond of CH 2 =CH–CN, followed by the formation of cyclic and linear intermediates that can undergo H, CN, and HCN elimination. In competition, the N( 2 D) addition to the CN group is also possible via a submerged barrier, leading ultimately to N 2 + C 3 H 3 formation, the most exothermic of all possible channels. Product angular and TOF distributions have been recorded for the H-displacement channels leading to the formation of a variety of possible C 3 H 2 N 2 isomeric products. Experimentally, no evidence of CN, HCN, and N 2 forming channels was observed. These findings were corroborated by the theory, which predicts a variety of competing product channels, following N( 2 D) addition to the double bond, with the main ones, at E c = 31.4 kJ/mol, being six isomeric H forming channels: c -CH(N)CHCN + H (BF = 35.0%), c -CHNCHCN + H (BF = 28.1%), CH 2 NCCN + H (BF = 26.3%), c -CH 2 (N)CCN(cyano-azirine) + H (BF = 7.4%), trans -HNCCHCN + H (BF = 1.6%), and cis -HNCCHCN + H (BF = 1.3%), while C–C bond breaking channels leading to c -CH 2 (N)CH(2H-azirine) + CN and c -CH 2 (N)C + HCN are predicted to be negligible (0.02% and 0.2%, respectively). The highly exothermic N 2 + CH 2 CCH (propargyl) channel is also predicted to be negligible because of the very high isomerization barrier from the initial addition intermedia...

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Section: Introductionmentioning

confidence: 62%

Section: Introductionmentioning

confidence: 71%

The N(²D) + CH₂CHCN (Vinyl Cyanide) Reaction: A Combined Crossed Molecular Beam and Theoretical Study and Implications for the Atmosphere of Titan

et al. 2022

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“…CMB results have always been complemented by electronic structure calculations of the relevant stationary points of the underlying potential energy surface (PES) and statistical (Rice-Ramsperger-Kassel-Marcus) calculations of the branching fractions. This combined theoretical and experimental approach was applied to the multichannel reactions N( 2 D) + CH 4 , C 2 H 2 , C 2 H 4 , and C 2 H 6 . − Much more recently, within the framework of the Italian National Project of Astrobiology, we conducted a combined experimental and theoretical investigation of the reaction of N( 2 D) with HCCCN (cyanoacetylene), C 5 H 5 N (pyridine), allene (unpublished results), C 6 H 6 (benzene), − and C 6 H 5 CH 3 (toluene) . In all cases, new species holding a novel C–N bond were identified as major reaction products, thus implying that N( 2 D) reactions with hydrocarbons are major players in the initiation of nitrile chemistry.…”

Section: Introductionmentioning

confidence: 99%

The Reaction N(²D) + CH₃CCH (Methylacetylene): A Combined Crossed Molecular Beams and Theoretical Investigation and Implications for the Atmosphere of Titan

et al. 2021

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The reaction of excited nitrogen atoms N( 2 D) with CH 3 CCH (methylacetylene) was investigated under single-collision conditions by the crossed molecular beams (CMB) scattering method with mass spectrometric detection and time-of-flight analysis at the collision energy ( E c ) of 31.0 kJ/mol. Synergistic electronic structure calculations of the doublet potential energy surface (PES) were performed to assist the interpretation of the experimental results and characterize the overall reaction micromechanism. Theoretically, the reaction is found to proceed via a barrierless addition of N( 2 D) to the carbon–carbon triple bond of CH 3 CCH and an insertion of N( 2 D) into the CH bond of the methyl group, followed by the formation of cyclic and linear intermediates that can undergo H, CH 3 , and C 2 H elimination or isomerize to other intermediates before unimolecularly decaying to a variety of products. Kinetic calculations for addition and insertion mechanisms and statistical (Rice-Ramsperger-Kassel-Marcus) computations of product branching fractions (BFs) on the theoretical PES were performed at different values of total energy, including the one corresponding to the temperature (175 K) of Titan’s stratosphere and that of the CMB experiment. Up to 14 competing product channels were statistically predicted, with the main ones, at E c = 31.0 kJ/mol, being the formation of CH 2 NH (methanimine) + C 2 H (ethylidyne) (BF = 0.41), c -C(N)CH + CH 3 (BF = 0.32), CH 2 CHCN (acrylonitrile) + H (BF = 0.12), and c -CH 2 C(N)CH + H (BF = 0.04). Of the 14 possible channels, seven correspond to H displacement channels of different exothermicity, for a total H channel BF of ∼0.25 at E c = 31.0 kJ/mol. Experimentally, dynamical information could only be obtained about the overall H channels. In particular, the experiment corroborates the formation of acrylonitrile + H, which is the most exothermic of all 14 reaction channels and is theoretically calculated to be the dominant H-forming channel (BF = 0.12). The products containing a novel C–N bond could be potential precursors to form other nitriles (C 2 N 2 , C 3 N) or more complex organic species containing N atoms in planetary atmospheres, such as those of Titan and Pluto. Overall, the results are expected to have a potentially significant impact on the understanding of the gas-phase chemistry of Titan’s atmosphere and the modeling of that atmosphere.

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“…It is of interest to compare the reaction dynamics of N( 2 D) + allene with that of the isomeric reaction N( 2 D) + methylacetylene recently studied in our laboratory at a comparable E c . 18 Methylacetylene and allene are structural isomers that are normally not distinguished in astrochemical or photochemical models, being simply indicated with their gross formula C 3 H 4 . However, it has been already noted that their formation and destruction routes are indeed different in many cases.…”

Section: Comparison With N( 2 D) + Ch 3 Cch (Methylacetylene)mentioning

confidence: 99%

“…Because of the difficulty in producing N( 2 D) in a controlled manner, until recently only fragmentary information was available from laboratory experiments on the reactions of N( 2 D). After detailed investigation by means of the crossed molecular beam (CMB) method, supported by electronic structure calculations of the underlying potential energy surface (PES), now we know that N( 2 D) has a complex chemical behavior, being able to insert into sigma bonds or to add to multiple bonds. − When reacting with hydrocarbons, molecular products possessing a novel C–N bond are formed. − ,− Recent kinetic experiments performed with the CRESU technique at the relevant temperature for the conditions of the upper atmosphere of Titan have revealed that the rate constants for several important N( 2 D) reactions are considerably larger , or smaller than those determined by previous experiments above 200 K. − The inclusion of these data in updated versions of a photochemical model of the atmosphere of Titan have demonstrated the importance of this approach in making the model more accurate. − …”

Section: Introductionmentioning

confidence: 99%

Reaction N(²D) + CH₂CCH₂ (Allene): An Experimental and Theoretical Investigation and Implications for the Photochemical Models of Titan

Vanuzzo

Mancini

Pannacci

et al. 2022

ACS Earth Space Chem.

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We report on a combined experimental and theoretical investigation of the N( 2 D) + CH 2 CCH 2 (allene) reaction of relevance in the atmospheric chemistry of Titan. Experimentally, the reaction was investigated (i) under singlecollision conditions by the crossed molecular beams (CMB) scattering method with mass spectrometric detection and time-offlight analysis at the collision energy (E c ) of 33 kJ/mol to determine the primary products and the reaction micromechanism and (ii) in a continuous supersonic flow reactor to determine the rate constant as a function of temperature from 50 to 296 K. Theoretically, electronic structure calculations of the doublet C 3 H 4 N potential energy surface (PES) were performed to assist the interpretation of the experimental results and characterize the overall reaction mechanism. The reaction is found to proceed via barrierless addition of N( 2 D) to one of the two equivalent carbon− carbon double bonds of CH 2 CCH 2 , followed by the formation of several cyclic and linear isomeric C 3 H 4 N intermediates that can undergo unimolecular decomposition to bimolecular products with elimination of H, CH 3 , HCN, HNC, and CN. The kinetic experiments confirm the barrierless nature of the reaction through the measurement of rate constants close to the gas-kinetic rate at all temperatures. Statistical estimates of product branching fractions (BFs) on the theoretical PES were carried out under the conditions of the CMB experiments at room temperature and at temperatures (94 and 175 K) relevant for Titan. Up to 14 competing product channels were statistically predicted with the main ones at E c = 33 kJ/mol being formation of cyclic-CH 2 C(N)CH + H (BF = 87.0%) followed by CHCCHNH + H (BF = 10.5%) and CH 2 CCNH + H (BF = 1.4%) the other 11 possible channels being negligible (BFs ranging from 0 to 0.5%). BFs under the other conditions are essentially unchanged. Experimental dynamical information could only be obtained on the overall H-displacement channel, while other possible channels could not be confirmed within the sensitivity of the method. This is also in line with theoretical predictions as the other possible channels are predicted to be negligible, including the HCN/HNC + C 2 H 3 (vinyl) channels (overall BF < 1%). The dynamics and product distributions are dramatically different with respect to those observed in the isomeric reaction N( 2 D) + CH 3 CCH (propyne), where at a similar E c the main product channels are CH 2 NH (methanimine) + C 2 H (BF = 41%), c-C(N)CH + CH 3 (BF = 32%), and CH 2 CHCN (vinyl cyanide) + H (BF = 12%). Rate coefficients (the recommended value is 1.7 (±0.2) × 10 −10 cm 3 s −1 over the 50−300 K range) and BFs have been used in a photochemical model of Titan's atmosphere to simulate the effect of the title reaction on the species abundance (including any new products formed) as a function of the altitude.

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Combined crossed molecular beams and computational study on the N(²D) + HCCCN(X¹Σ⁺) reaction and implications for extra-terrestrial environments

Cited by 12 publications

References 82 publications

The N(²D) + CH₂CHCN (Vinyl Cyanide) Reaction: A Combined Crossed Molecular Beam and Theoretical Study and Implications for the Atmosphere of Titan

The N(²D) + CH₂CHCN (Vinyl Cyanide) Reaction: A Combined Crossed Molecular Beam and Theoretical Study and Implications for the Atmosphere of Titan

The Reaction N(²D) + CH₃CCH (Methylacetylene): A Combined Crossed Molecular Beams and Theoretical Investigation and Implications for the Atmosphere of Titan

Reaction N(²D) + CH₂CCH₂ (Allene): An Experimental and Theoretical Investigation and Implications for the Photochemical Models of Titan

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Combined crossed molecular beams and computational study on the N(2D) + HCCCN(X1Σ+) reaction and implications for extra-terrestrial environments

Cited by 12 publications

References 82 publications

The N(2D) + CH2CHCN (Vinyl Cyanide) Reaction: A Combined Crossed Molecular Beam and Theoretical Study and Implications for the Atmosphere of Titan

The N(2D) + CH2CHCN (Vinyl Cyanide) Reaction: A Combined Crossed Molecular Beam and Theoretical Study and Implications for the Atmosphere of Titan

The Reaction N(2D) + CH3CCH (Methylacetylene): A Combined Crossed Molecular Beams and Theoretical Investigation and Implications for the Atmosphere of Titan

Reaction N(2D) + CH2CCH2 (Allene): An Experimental and Theoretical Investigation and Implications for the Photochemical Models of Titan

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Combined crossed molecular beams and computational study on the N(²D) + HCCCN(X¹Σ⁺) reaction and implications for extra-terrestrial environments

The N(²D) + CH₂CHCN (Vinyl Cyanide) Reaction: A Combined Crossed Molecular Beam and Theoretical Study and Implications for the Atmosphere of Titan

The N(²D) + CH₂CHCN (Vinyl Cyanide) Reaction: A Combined Crossed Molecular Beam and Theoretical Study and Implications for the Atmosphere of Titan

The Reaction N(²D) + CH₃CCH (Methylacetylene): A Combined Crossed Molecular Beams and Theoretical Investigation and Implications for the Atmosphere of Titan

Reaction N(²D) + CH₂CCH₂ (Allene): An Experimental and Theoretical Investigation and Implications for the Photochemical Models of Titan