FT-IR measurements of cold propene (C3H6) cross-sections at temperatures between 150 and 299 K

Abstract

In support of infrared remote sensing of Titan, we present temperature dependent cross-sections of propene (C3H6; CH2CHCH3; propylene) measured in the laboratory. A total of 27 high-resolution (up to 0.0022 cm−1) spectra of pure C3H6 and mixtures of C3H6 with N2 were obtained at 150–299 K in the 650–1534 cm−1 (6.5–15.4 µm) region. A custom-designed cold cell was used, which was configured with an active temperature control and could be integrated to a Fourier-transform spectrometer (Bruker 125HR) at the Jet Propulsion Laboratory. The observed C3H6 spectral features include its strong v19 band bearing the most prominent Q-branch peak at 912 cm−1 and three other strong bands: v18, v16 and v7 centered near 991, 1443, and 1459 cm−1, respectively. In addition, we have generated empirical pseudoline lists (PLLs) in HITRAN-format, in the two separate spectral regions, which are Region I: 800–1100 and Region II: 1340–1524 cm−1. The PLLs of C3H6 consists of spectroscopic line parameters (including line intensities and effective lower state energies) for all the individual pseudoline positions. The pseudoline parameters were determined by fitting 27 laboratory spectra of pure and N2-broadened propene simultaneously in the selected regions. A newly derived partition function was adopted in the line-by-line radiative transfer calculations. Based on the pseudoline intensities, the total integrated intensities in the 800–1120 and 1320–1524cm−1 regions were measured to be 8.79(47)× 10−18 and 3.06(21)×10−18cm−1/(molecule cm−2) at 296 K, respectively. These values are found to be in a good agreement with the recent measurement made at KAUST at room temperature, but they are significantly lower than those reported by one of the most extensive previous studies at the Pacific Northwest National Laboratory (PNNL). Finally, the two PLLs are submitted as electronic supplements and are also available from the website, https://mark4sun.jpl.nasa.gov/pseudo.html.