The 1.5 μm Band of Cyanoacetylene as a Spectroscopic Target in Astrochemistry

The search for prebiotic molecules officially entered a new era with the launch of the James Webb Space Telescope. The capabilities of the near-infrared instrumentation on board offer greater sensitivity and resolution than have ever been available in a space-based instrument. With the planned launch of more near-infrared telescopes, such as SPHEREx in 2025, it is essential to have laboratory data for important molecules on hand to guide observations in this spectral region. We present here the first published line list of the prebiotic cyanoacetylene (HC₃N) molecule in the 1.5 μm region. Molecules were cooled to 20 K through the use of cryogenic buffer-gas cooling yielding well-resolved ro-vibrational states of the 2ν₁ band that were probed and assigned using cavity-ringdown spectroscopy. Rotational constants were calculated using PGOPHER, and spectral line intensities were measured relative to hydrogen cyanide. We recommend the HC₃N 1.5 μm band as an observational target for transmission spectroscopy at Hycean and Super-Earth exoplanetary bodies.