Astrophys. J., 742, 26 (2011/November-3)
A crossed molecular beam, low-temperature kinetics, and theoretical investigation of the reaction of the cyano radical (CN) with 1,3-butadiene (C4H6). A route to complex nitrogen-bearing molecules in low-temperature extraterrestrial environments.
MORALES S.B., BENNETT C.J., LE PICARD S.D., CANOSA A., SIMS I.R., SUN B.J., CHEN P.H., CHANG A.H.H., KISLOV V.V., MEBEL A.M., GU X., ZHANG F., MAKSYUTENKO P. and KAISER R.I.
Abstract (from CDS):
We present a joint crossed molecular beam and kinetics investigation combined with electronic structure and statistical calculations on the reaction of the ground-state cyano radical, CN(X 2Σ+), with the 1,3-butadiene molecule, H2CCHCHCH2(X 1 Ag), and its partially deuterated counterparts, H2CCDCDCH2(X 1 Ag) and D2CCHCHCD2(X 1 Ag). The crossed beam studies indicate that the reaction proceeds via a long-lived C5H6N complex, yielding C5H5 N isomer(s) plus atomic hydrogen under single collision conditions as the nascent product(s). Experiments with the partially deuterated 1,3-butadienes indicate that the atomic hydrogen loss originates from one of the terminal carbon atoms of 1,3-butadiene. A combination of the experimental data with electronic structure calculations suggests that the thermodynamically less favorable 1-cyano-1,3-butadiene isomer represents the dominant reaction product; possible minor contributions of less than a few percent from the aromatic pyridine molecule might be feasible. Low-temperature kinetics studies demonstrate that the overall reaction is very fast from room temperature down to 23 K with rate coefficients close to the gas kinetic limit. This finding, combined with theoretical calculations, indicates that the reaction proceeds on an entrance barrier-less potential energy surface (PES). This combined experimental and theoretical approach represents an important step toward a systematic understanding of the formation of complex, nitrogen-bearing molecules–here on the C5H6 N PES–in low-temperature extraterrestrial environments. These results are compared to the reaction dynamics of D1-ethynyl radicals (C2D; X 2Σ+) with 1,3-butadiene accessing the isoelectronic C6H7 surface as tackled earlier in our laboratories.
astrochemistry - methods: laboratory - molecular processes
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