Measurements of the Reaction Rate Coefficients of Atomic Hydrogen with Astrochemical Anions: CN− and C3N−

Abstract

We present the temperature-dependent reaction rate coefficients of CN ^− and C _3 N ^− with atomic hydrogen in the temperature range from 7 to 290 K, measured in a 16-pole radio-frequency ion trap. The rate of C _3 N ^− with H steadily increases toward lower temperatures, while the rate coefficients for the CN ^− + H system show a sudden change around 160 K. Fits to the data were performed to determine temperature-dependent reaction rate coefficients. The fits reveal a rate coefficient of $4.1{(3)\times {10}^{-10}(T/300)}^{-0.31(6)}$ cm ^3 s ^−1 for C _3 N ^− + H. For CN ^− , we determined a rate coefficient for the temperature regime below 160 K of $3.2{(4)\times {10}^{-10}(T/300)}^{-0.31(11)}$ cm ^3 s ^−1 . Given our present results, higher rate coefficients than previously reported must be assumed for the modeling of cold interstellar environments involving these H atom reactions.

Keywords

• Interstellar clouds
• Laboratory astrophysics
• Ion-neutral reactions