Synthesis of Cyanide Ions (CN-) via Hypervelocity Impacts (HVIs)

Hypervelocity impacts (HVIs), often considered catastrophic processes, may have a profound role in the emergence of life on planetary systems as the energy deposited during HVI events enables molecular rearrangement (via ionization and recombination) and the synthesis of essential prebiotic compounds. Hydrogen cyanide (HCN) is a particularly important prebiotic building block for polymerizing complex organic macromolecules (i.e., protein and DNA) due to its reactivity (cyano radicals) and stable structure (triple bonds). While previous HVI experiments have synthesized cyanide ions (CN^-) from graphite or methane in a reducing atmosphere (primarily N₂ ± CO₂), this research aims to investigate the chemical consequences and biological implications of meteorite impact events on salt- and carbonate-bearing planetary surfaces in vacuum. In the laboratory, high energy laser pulses (i.e., fluences > 10 J/cm2) simulate extreme plasma conditions analogous to those incurred via HVIs, thereby allowing for the characterization of complex chemical reactions under representative conditions.

The experimental objectives for our specific study are: (1) synthesize CN^- from inorganic sources, specifically mixtures of powdered calcium carbonate (CaCO₃) and N-containing salts, via pulsed laser irradiation in vacuum (i.e., ≤ 1E-6 Pa); and, (2) characterize the effects of oxidation states of the nitrogenous reactant. The experiments were performed at NASA Goddard Space Flight Center (GSFC) using a Hiden quadrupole mass analyzer interfaced to a Q-smart 1064 nm pulsed laser system (35 mJ maximum energy output, 9 ns pulse width). The sample substrate, a combination of reagent-grade CaCO₃ and one of two N-containing salts (NH₄Cl versus NaNO₃), were physically admixed and compressed to represent a common lithology found on rocky planetary bodies (e.g., Vesta). Carbonate doped with ¹³C, and N-containing salts doped with ¹⁵N, were used to isolate potential isobaric interferences and validate the signal peak of CN^-. Our results show a correlation between the concentration of reactants and peak heights of CN^- at their doped and undoped mass station. Semi-quantitative analyses indicate that yields of CN^- are higher with a more oxidizing nitrogen source, an apparent contradiction to other studies of abiotic organic synthesis.