A case study on photostability of biologically relevant anions under structural modifications

ABSTRACT The interstellar medium (ISM) hosts a wide range of molecular species, including those considered to be precursors of biologically relevant compounds. Laboratory experiments demonstrate that intermediates such as carbamic acid can form on cold interstellar grain surfaces and their identification in meteorites and comets provides evidence for their origin in the ISM or the early solar system. However, these molecules can undergo photodestruction in the ISM, making their photostability a critical characteristic to be examined in the laboratories. In this work, we examine the gas-phase photostability of deprotonated indole-based molecules, tryptophan, 7-azaindole, and 3-azaindole, as analogues of complex space organics. Indole is the side chain of tryptophan, and azaindoles are nitrogen-containing heterocycles that serve as relevant analogues for complex organics potentially present in space. Using a novel laboratory methodology, we report the first absolute photodetachment cross-section measurements at 403 nm for these anions, providing quantitative constraints on their resilience to photon-induced electron loss. While wavelength-dependent measurements would offer broader coverage, the present results establish a critical benchmark for astrochemical models and serve as a reference for future experimental and theoretical studies.