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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>4.1</mml:mn> <mml:msup> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:mn>3</mml:mn> <mml:mo stretchy="false">)</mml:mo> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>10</mml:mn> </mml:mrow> </mml:msup> <mml:mo stretchy="false">(</mml:mo> <mml:mi>T</mml:mi> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mn>300</mml:mn> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.31</mml:mn> <mml:mo stretchy="false">(</mml:mo> <mml:mn>6</mml:mn> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> </mml:msup> </mml:math> cm 3 s −1 for C 3 N − + H. For CN − , we determined a rate coefficient for the temperature regime below 160 K of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>3.2</mml:mn> <mml:msup> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:mn>4</mml:mn> <mml:mo stretchy="false">)</mml:mo> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>10</mml:mn> </mml:mrow> </mml:msup> <mml:mo stretchy="false">(</mml:mo> <mml:mi>T</mml:mi> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mn>300</mml:mn> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.31</mml:mn> <mml:mo stretchy="false">(</mml:mo> <mml:mn>11</mml:mn> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> </mml:msup> </mml:math> 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.