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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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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...