Updated Polyyne Chemistry for Polyyne Polymerization and Organic Aerosol Synthesis in the Atmosphere of Titan
Abstract
For the last four decades, the role of polyynes such as diacetylene and triacetylene in the chemical evolution of the atmosphere of Saturn's moon Titan has been a subject of vigorous research. These polyacetylenes are thought to serve as an ultraviolet radiation shield in planetary environments thus acting as prebiotic ozone and are considered as important constituents of the visible haze layers on Titan. However, the underlying chemical processes which initiate the formation and control the growth of polyynes have been the least understood to date. Here we present preliminary results of including postulated chemistry into a photochemical model for Titan. The insertion reactions exhibit no entrance barrier, are exothermic, and all transition states, which are involved, are below the energy of the reactant molecules. Due to these characteristics, the elementary reaction of the ethynyl radical with diacetylene represents an efficient pathway to produce triacetylene in Titan's atmosphere in those regions where density profiles of photolytically generated ethynyl radicals and diacetylene overlap. Our models of Titan's atmosphere indicate that successive reactions of the triacetylene molecule can yield even more complex polyynes. Here, ethynyl radicals (CCH) or 1,4-butadiynyl radicals (HCCCC), formed via photodissociation of acetylene and diacetylene, respectively, can react with triacetylene to tetraacetylene (C8H2) and pentaacetylene (C10H2), respectively. This offers important sinks for triacetylene and produces potential polyyne precursors for the organic aerosol layers.
- Publication:
-
EPSC-DPS Joint Meeting 2011
- Pub Date:
- October 2011
- Bibcode:
- 2011epsc.conf..940L