Laboratory studies of low-temperature reactions of ethynyl with acetylene and implications for atmospheric models of Titan

Direct measurements of rate coefficients for the reaction of ethynyl radical (C2H) with C2H2 at 90 and 120 K using a pulsed Laval nozzle apparatus

“…The possible products of C2H 2 photolysis, such as roetastable acetylene, C2H 2 , electronically and vibrationally excited C2 H, and C2, were extensively discussed [Pedersen et al, 1993]. In our earlier flow tube work [Pedersen et al, 1993], it was found that the C2H production was proportional to the excimer pulse energy up to 130 mJ/pulse. Furthermore, the N 2 carrier gas quenches electronically and vibrationally excited C2H to the ground state.…”

“…The photochemical primary process in C2H 2 is known to be fairly complex [Koshi et al, 1992b, and references therein]. The possible products of C2H 2 photolysis, such as roetastable acetylene, C2H 2 , electronically and vibrationally excited C2 H, and C2, were extensively discussed [Pedersen et al, 1993]. In our earlier flow tube work [Pedersen et al, 1993], it was found that the C2H production was proportional to the excimer pulse energy up to 130 mJ/pulse.…”

“…Our earlier work [Pedersen et al, 1993;Opansky and Leone, 1996] provided detailed measurements of (R1) down to 143 K using transient infrared laser absorption spectroscopy in a lowtemperature flow cell. Temperature-dependent rate constants were found to show a slight negative temperature dependence.…”

H elimination and metastable lifetimes in the UV photoexcitation of diacetylene

“…Diacetylene is believed to play a key role in the formation of polyynes and polycyclic aromatic hydrocarbons (PAHs) that partially comprise the haze layer in Titan's upper atmosphere (2)(3)(4). It is well established that the formation of diacetylene is initiated by photodissociation of acetylene below 217 nm (2,(5)(6)(7)(8) according to the following reaction mechanism: C 2 H 2 ϩ hv ¡ C 2 H ϩ H͑ Ͻ 217 nm͒ C 2 H ϩ C 2 H 2 ¡ C 4 H 2 ϩ H The importance ascribed to diacetylene arises in part because it absorbs light at longer wavelengths, where the solar flux is higher, than any other major constituents of Titan's atmosphere; moreover, experimental results suggest it is still photochemically reactive even well below the threshold for dissociation (9)(10)(11)(12). Understanding the dynamics of diacetylene photoexcitation is thus key to revealing the factors driving the chemistry of Titan's atmosphere.…”

Ab Initio Quantum Chemical Studies on Neutral-Radical Reactions of Ethynyl (C2H) and Cyano (CN) with Unsaturated Hydrocarbons

“…The radical addition can occur to several possible sites on an unsaturated hydrocarbon, yielding a vast amount of larger, more complex products that can result. [23][24][25][26][27][28][29][30][31][32][33][34][35][55][56][57][58][59][60][61][62][63][64] The products are generated either immediately upon the radical addition to the unsaturated hydrocarbon or through various isomerization steps including cyclizations, followed by an atom or polyatomic group loss.…”