Photochemistry of acetylene, hydrogen cyanide, and mixtures

Abstract

In" I Flgure 8. The inversion of experimental argon-graphite second virial coefficients. The data points refer to different initial approxlmate potentials: (0) 9-3; (0) 9-3.5; (A) Steele. The solid lines show the 9-3.3 and 9-3.5 potentials. tained by the minimization procedure outlined above. The value of tIS used in this study was instead taken from Steele's analysis of graphite-rare gas interactions using the "summed 10-4" p~t e n t i a l .~ This gives qs = 959 K for the argon-gr aphi te system.The smoothed experimental data were inverted by use of a range of suitable approximate potentials to calculate G@)(T*), as shown in Figure 6. The results show a clear convergence from the common potential functionality with an attractive exponent of 3.4 f 0.1. However, this convergence is slow due to the sensitivity of the inverted potential to the initial approximate potential in this range of separations. ConclusionsThe inversion method proposed is clearly of value when data of sufficient accuracy and temperature range are available. With the low-temperature data currently available a successful inversion requires both an initial approximate potential which closely resembles the true potential and an accurate, independent estimate of tIS. The inversion of this low-temperature data can be used to establish upper and lower bounds to the long-range behavior of the gas-surface interaction. In general, however, to realize the full potential of the inversion method we require measurements over a larger temperature range. For the argon-graphite system, in order to define the potential function over the main region of interest without resorting to additional data we would need the low pressure adsorption isotherms at temperatures up to 1500 K. Acknowledgment. The authors thank Professors W. A.Photolyses of HCN, C2H2, and mixtures were accomplished including various ratios of HCN/C2H2 and time periods. The photolysis of HCN yielded (CN),, CHI, NH3, CH3NH2, (NH),, and a brown polymer. The products from C2H, were diacetylene (C4H,), CzH4, C6&, vinylacetylene, phenylacetylene, and a polymer. Products from a relatively low HCN/CzHz ratio (51) where 90% of the light is absorbed by CzHz were similar to those of C2Hz except for the additional formation of acrylonitrile (C2H3CN). At relatively higher ratios of HCN/C2Hz where 37-56% of the light is absorbed by HCN, cyanoacetylene (C,HCN) was formed in addition to the foregoing products and the C4Hz substantially reduced. The proposed principal path for formation of C4HZ is attack of C2H. on C2H2, while for C2H3CN the principal path is attack of CzH3. on HCN. The proposed principal path for production of CzHCN is via CN. attack on C2H2. Several products from HCN are proposed to be the result of progressive H atom addition. Other products from CzHz and HCN are the result of radical-radical recombination. We believe these results could have relevance to Jovian atmosphere chemistry and formation of several molecules found in interstellar space.

Photochemical processes on Titan: Irradiation of mixtures of gases that simulate Titan's atmosphere

“…The high quantum yields for cyanoacetylene loss and hydrogen cyanide formation appear to be in conflict with the proposed photochemical synthesis of cyanoacetylene by irradiation of hydrogen cyanide-acetylene mixtures (Becker and Hong, 1983). This conflict is resolved by the requirement of a 10:1 or greater hydrogen cyanide:acetylene ratio to form cyanoacetylene, a ratio significantly greater than observed in Titan's atmosphere.…”

“…Acrylonitrile was also observed as a product of the photolysis of 5:1 mixture of acetylene and hydrogen cyanide (Becker and Hong, 1983). It is possible that very small amounts of acrylonitrile, formed by the action of solar UV, are present in Titan's atmosphere.…”

Rate coefficients for reactions of ethynyl radical (C2H) with HCN and CH3CN: Implications for the formation of complex nitriles on Titan

“…There has been one previous study that examined only the overall product photochemistry of acetylene and hydrogen cyanide mixtures [Becker and Hong, 1983]. In those experiments, photolysis of C2H 2 and HCN mixtures were exposed to 185 nm light from a low-pressure mercury lamp (10 7 photons/s) for 2 min.…”

Hydrogen cyanide in nitrogen-rich atmospheres of rocky exoplanets

“…This choice of rate constant will be justified in Section 4.2. Finally, we have added the reaction (Becker and Hong, 1983):…”