Floating Patches of HCN at the Surface of Their Aqueous Solutions - Can They Make "HCN World" Plausible?

The liquid/vapor interface of the aqueous solutions of HCN of different concentrations has been investigated using molecular dynamics simulation and intrinsic surface analysis. Although HCN is fully miscible with water, strong interfacial adsorption of HCN is observed at the surface of its aqueous solutions, and, at the liquid surface, the HCN molecules tend to be located even at the outer edge of the surface layer. It turns out that in dilute systems the HCN concentration can be about an order of magnitude larger in the surface layer than in the bulk liquid phase. Furthermore, HCN molecules show a strong lateral self-association behavior at the liquid surface, forming thus floating HCN patches at the surface of their aqueous solutions. Moreover, HCN molecules are staying, on average, an order of magnitude longer at the liquid surface than water molecules, and this behavior is more pronounced at smaller HCN concentrations. Because of this enhanced dynamical stability, the floating HCN patches can provide excellent spots for polymerization of HCN, which can be the key step in the prebiotic synthesis of partially water-soluble adenine. All of these findings make the hypothesis of "HCN world" more plausible

Products and mechanism of the OH-initiated photo-oxidation of perfluoro ethyl vinyl ether, C 2 F 5 OCF=CF 2

The OH-initiated photo-oxidation of perfluoro ethyl vinyl ether (C2F5OCF[double bond, length as m-dash]CF2, PEVE) in air (298 K, 50 and 750 Torr total pressure) was studied in a photochemical reactor using in situ detection of PEVE and its products by Fourier transform IR absorption spectroscopy. The relative rate technique was used to derive the rate coefficient, k1, for the reaction of PEVE with OH as k1 = (2.8 ± 0.3) × 10−12 cm3 molecule−1 s−1. The photo-oxidation of PEVE in the presence of NOx at 1 bar results in formation of C2F5OCFO, FC(O)C(O)F and CF2O in molar yields of 0.50 ± 0.07, 0.46 ± 0.07 and 1.50 ± 0.22, respectively. FC(O)C(O)F and CF2O are formed partially in secondary, most likely heterogeneous processes. At a reduced pressure of 50 Torr, the product distribution is shifted towards formation of FC(O)C(O)F, indicating the important role of collisional quenching of initially formed association complexes, and enabling details of the reaction mechanism to be elucidated. An atmospheric photo-oxidation mechanism for PEVE is presented and the environmental implications of PEVE release and degradation are discussed

Gas-Phase Reactions of OH with Methyl Amines in the Presence or Absence of Molecular Oxygen. An Experimental and Theoretical Study

The rate coefficients for the reaction of OH with the alkyl amines: methylamine (MA), dimethylamine (DMA), trimethylamine (TMA), and ethylamine (EA) have been determined using the technique of pulsed laser photolysis with detection of OH by laser-induced fluorescence as a function of temperature from 298 K to ∼600 K. The rate coefficients (10¹¹ × <i>k</i>/cm³ molecule^–1 s^–1) at 298 K in nitrogen bath gas (typically 5–25 Torr) are: <i>k</i>_OH+MA = 1.97 ± 0.11, <i>k</i>_OH+DMA = 6.27 ± 0.63, <i>k</i>_OH+TMA = 5.78 ± 0.48, <i>k</i>_OH+EA = 2.50 ± 0.13. The reactions all show a negative temperature dependence which can be characterized as: <i>k</i>_OH+MA = (1.889 ± 0.053) × 10^–11(<i>T</i>/298 K)^{−(0.56±0.10)}, <i>k</i>_OH+DMA = (6.39 ± 0.35) × 10^–11(<i>T</i>/298 K)^{−(0.75±0.18)}, <i>k</i>_OH+TMA = (5.73 ± 0.15) × 10^–11(<i>T</i>/298 K)^{−(0.71±0.10)}, and <i>k</i>_OH+EA = (2.54 ± 0.08) × 10^–11(<i>T</i>/298 K)^{−(0.68±0.10)}. OH and OD reactions have very similar kinetics. Potential energy surfaces (PES) for the reactions have been characterized at the MP2/aug-cc-pVTZ level and improved single point energies of stationary points obtained in CCSD­(T) and CCSD­(T*)-F12a calculations. The PES for all reactions are characterized by the formation of pre- and post-reaction complexes and submerged barriers. The calculated rate coefficients are in good agreement with experiment; the overall rate coefficients are relatively insensitive to variations of the barrier heights within typical chemical accuracy, but the branching ratios vary significantly. The rate coefficients for the reactions of OH/OD with MA, DMA, and EA do not vary with added oxygen, but for TMA a significant reduction in the rate coefficient is observed consistent with OH recycling from a chemically activated peroxy radical. OH regeneration is pressure-dependent and is not significant at 298 K and atmospheric pressure, but the efficiency of recycling increases strongly with temperature. The PES for OH recycling have been calculated. There is evidence that the primary process in TMA photolysis at 248 nm is the loss of H atoms