Amino acids produced from the ultraviolet/extreme-ultraviolet irradiation of naphthalene in a H₂O+NH₃ ice mixture

In this work, we show that the irradiation of naphthalene (C ₁₀H₈), the smallest polycyclic aromatic hydrocarbon (PAH), mixed in a H₂O+NH₃ ice mixture with 4-20 eV (62-310 nm, i.e. in the ultraviolet/extreme-ultraviolet ranges) photons at 15 K leads to the formation of an organic residue where many amino acids were identified. However, the distribution of these amino acids is different from what was reported in previous laboratory experiments where ice mixtures containing other sources of carbon (CO, CO₂, CH₄ and CH₃OH) were irradiated with ultraviolet photons, indicating that amino acids can be formed via several mechanisms. This result also implies that naphthalene, and probably other PAHs, constitute a non-negligible source of interstellar carbon likely to form organic molecules after photolysis, supporting a scenario where molecules of biological interest could be formed in many different astrophysical environments before being delivered to the early Earth by meteorites.