A crossed molecular beams study of the reaction of the ethynyl radical (C2H(X2Σ+)) with allene (H2CCCH2(X1A1))

Abstract

The crossed beams reaction of ground state ethynyl radicals, C(2)H(X(2)Sigma(+)), with allene, H(2)CCCH(2)(X(1)A(1)), was conducted under single collision conditions at a collision energy of 22.0 +/- 0.4 kJ mol(-1). The center-of-mass functions were combined with earlier ab initio calculations and revealed that the reaction was barrier-less, proceeded via indirect reaction dynamics through an addition of the ethynyl radical to the terminal carbon atom of the allene molecule, and was terminated by atomic hydrogen emission via a tight exit transition state to form the ethynylallene product. The overall reaction was found to be exoergic by 93 +/- 15 kJ mol(-1). Since the reaction is barrier-less, exoergic, and all transition states involved are located below the energy level of the separated reactants, the formation of ethynylallene is predicted to take place in low temperature atmospheres of planets and their satellites such as Titan and also in cold molecular clouds via the neutral-neutral reaction of ethynyl radicals with allene. Implications to interstellar chemistry and a comparison with the chemistry of the isoelectronic cyano radical, CN(X(2)Sigma(+)), are also presented.

Reaction of the C2H Radical with 1-Butyne (C4H6): Low-Temperature Kinetics and Isomer-Specific Product Detection

“…11,[13][14][15][16][17][18][19][20][21][22][23][24][25][26] In order to analyze and account for the presence of hydrocarbon species, modeling studies are of central importance in understanding the complex nature of Titan's atmosphere.…”

COMPLEX HYDROCARBON CHEMISTRY IN INTERSTELLAR AND SOLAR SYSTEM ICES REVEALED: A COMBINED INFRARED SPECTROSCOPY AND REFLECTRON TIME-OF-FLIGHT MASS SPECTROMETRY ANALYSIS OF ETHANE (C2H6) AND D6-ETHANE (C2D6) ICES EXPOSED TO IONIZING RADIATION

“…The C 3 H 4 isomer methylacetylene (CH 3 CCH; IE = 10.36 eV) isomer has been detected in a few astronomical surveys toward SgrB2, PKS 1830-211, L1544, and tentatively in NCG 4418 (Belloche et al 2013;Muller et al 2014;Vastel et al 2014;Costagliola et al 2015). Methylacetylene and its isomer allene (H 2 CCCH 2 ; IE = 9.69 eV) have been reactants in attempts to untangle the chemistry taking place in Titanʼs atmosphere (Vakhtin et al 2001;Goulay et al 2007;Zhang et al 2009). …”

“…Further, the C 3 H 4 isomers methylacetylene (CH 3 CCH) and allene (H 2 CCCH 2 ) represent two astrophysically important molecules that belong to the -C H n n 2 2 group. Besides playing roles in Titanʼs atmospheric chemistry (Vakhtin et al 2001;Goulay et al 2007;Zhang et al 2009) these isomers have been proven to be very important in interstellar chemistry. Specifically, both isomers are proposed to assist in the formation of PAHs (Yang et al 2015) and in particular of indene (C 9 H 8 ) in the reaction with the phenyl radical (C 6 H 5 ) Parker et al 2015Parker et al , 2011.…”

Reaction Dynamics of Carbon‐Centered Radicals in Extreme Environments Studied by the Crossed Molecular Beam Technique

“…In the primary source, a pulsed beam of open unstable (open shell) species is generated by laser ablation (C, C 2 , C 3 ), 117 laser ablation coupled with in situ reaction (CN, C 2 D), 98,118 photolysis (C 2 H, C 2 H 3 , C 3 H 3 ), 109,119,120 or flash pyrolysis (C 3 H 5 , C 6 H 5 ). 121,122 The pulsed primary beam is passed through a skimmer into the main chamber; a chopper wheel located after the skimmer and prior to the collision center selects a slice of species with well-defined velocity that reach the interaction region.…”

“…Typically, these are bromide or iodide precursors such as bromoacetylene (C 2 HBr), 119 vinyl bromide (C 2 H 3 Br), 120 and propargyl bromide (C 3 H 3 Br) 109 to yield supersonic beams of helium-seeded ethynyl, vinyl, and propargyl radicals, respectively. Briefly, the radical precursor is entrained in helium at a ratio of typically 1%.…”