Near- and mid-infrared spectroscopy of isobutyronitrile and cyanopropyne: absorption cross-sections for quantitative detection in astrophysical objects

Absorption cross-sections at room temperature have been derived for two non-cyclic organic molecules cyanopropyne (CH₃C₃N) and isobutyronitrile (i-C₃H₇CN), and have been proposed for the 2024 update of the high-resolution transmission molecular absorption database (HITRAN). The gas phase infrared spectra of pure cyanopropyne and isobutyronitrile have been recorded at room temperature between 160 and 3500 cm^-1 (3–60 µm) using an infrared Fourier transform spectrometer. The spectral resolution has been chosen equal to 0.056 cm^-1. For the 18–20 µm spectral region an additional resolution equal to 0.01 cm^-1 has been used. Among the various absorption bands observed, some of them, as the ν₁₀ band of cyanopropyne around 500 cm^-1 (20 µm), are particularly interesting for detecting and quantifying these molecules in astrophysical objects. As a first application, the retrieved absorption cross-sections have been used in a radiative transfer code to simulate observations of Titan's stratosphere acquired using the Texas Echelon Cross Echelle Spectrograph (TEXES at the Infrared Telescope Facility (IRTF, Mauna Kea Observatory). We discuss preliminary results and perspectives, among which estimated upper limits of 3 × 10^–9 for cyanopropyne and 3 × 10^–7 for isobutyronitrile in Titan's stratosphere.