Crossed molecular beam study of gas phase reactions relevant to the chemistry of planetary atmospheres: The case of C 2+C 2H 2

Abstract

The reaction between dicarbon (C 2) and acetylene was recently suggested as a possible competitive reaction in the atmospheres of Titan, Saturn and Uranus by rate constant measurements at very low temperatures [see Canosa, A., Páramo, A., Le Picard, S.D., Sims, I.R., 2007. An experimental study of the reaction kinetics of C 2(X 1Σ g +) with hydrocarbons (CH 4, C 2H 2, C 2H 4, C 2H 6 and C 3H 8) over the temperature range 24–300 K: implications for the atmospheres of Titan and the Giant Planets. Icarus 187, 558–568]. We have investigated the reaction of the two low lying electron states of C 2 and acetylene by the crossed molecular beam (CMB) technique with mass spectrometric detection. C 4H, already identified as a primary product in previous CMB experiments, is confirmed as such, even though the mechanism of formation is inferred to be partly different with respect to the previous study. An experimental setup has been devised to characterize the internal population of C 2 and refine the interpretation of the scattering results. The implications for the modelling of the atmospheres of Giant Planets and Titan, as well as cometary comae and the interstellar medium, are discussed.