Formation of Gas-Phase Glycine and Cyanoacetylene via Associative Detachment Reactions

Abstract

The recent discovery of molecular negative ions in the interstellar medium suggests that these species may be reactive intermediates in astrochemical processes. Our recent studies indicate that these anions, despite their high electron binding energies, are reactive with atomic reagents. In this work, we report that two species of interstellar interest, glycine (NH₂CH₂COOH) and cyanoacetylene (HC₃N), can be readily formed by associative detachment of their corresponding deprotonated anions with hydrogen atoms. The reaction rate constants for glycine anion (NH₂CH₂CO₂ ⁻) and cyanoacetylene anion (C₃N⁻) with H atom have been measured to be 2.0 ± 0.5 ×10⁻¹⁰ cm³ s⁻¹ and 5.4 ± 0.2 × 10⁻¹⁰ cm³ s⁻¹, respectively, where the error bars represent one standard deviation of the mean; the estimated total error is ± 50%. A possible reaction mechanism for chemical conversion of species observed in the interstellar medium is also described. Key Words: Astrochemistry—Negative ions—Ion chemistry—Associative detachment. Astrobiology 9, 1001–1005.