Pseudoline parameters to represent n-butane (n-C4H10) cross-sections measured in the 7–15 µm region for the Titan atmosphere. (August 2020)

• Record Type: Journal Article
• Authors: Sung, Keeyoon; Steffens, Brendan; Toon, Geoffrey C.; Nemchick, Deacon J.; Smith, Mary Ann H.
• Is Part Of: Journal of quantitative spectroscopy & radiative transfer. Volume 251(2020)
• Publication Date: 2020-08
• Subjects: n-Butane -- FT-IR spectrum -- Cross section -- Pseudolines -- Bruker 125HR -- Cassini/CIRS -- Titan -- Hydrocarbons; Spectrum analysis -- Periodicals; Radiation -- Periodicals; Analyse spectrale -- Périodiques; Rayonnement -- Périodiques; Radiation; Spectrum analysis; Periodicals; 543.0858
• DOI: 10.1016/j.jqsrt.2020.107011
• Languages: English
• ISSNs: 0022-4073

Abstract

Highlights: Obtained 28 spectra of n-C4 H10 at 180 – 298 K from 650 to 1538 cm −1 using a FT-IR at JPL. Derived cross-sections of n-C4 H10 as a function of wavenumber and temperature. Generated pseudoline lists to represent the observed spectra to within 5% or better. Measured integrated intensities to be 5.06(28), 7.18(27), 0.91(4), and 49.01(20) × 10 −19 cm −1 /(molecule.cm −2 ) in the 660–860, 860–1060, 1060–1200, and 1200–1538 cm −1 regions respectively. Abstract: We measured temperature-dependent cross-sections of n-butane (CH3 CH2 CH2 CH3 ) in the mid-infrared (7–15 μm) region in support of remote sensing for the Titan's atmosphere. For this, 28 pure and N2 -mixture spectra were obtained at 180–298 K using a high-resolution Fourier transform spectrometer (Bruker IFS 125 HR) at the Jet Propulsion Laboratory. The spectral resolutions were selected to be between 0.0039 and 0.06 cm −1, depending on the sample pressures. The observed spectra were fit simultaneously to generate one single set of pseudolines, which include line intensities and lower state energies at individual pseudoline positions. The observed spectra could be reproduced by the pseudolines to within 4% through line-by-line radiative transfer calculations. The integrated intensities at 296 K were measured to be 5.06(28), 7.18(27), 0.91(4), and 49.01(20) × 10 −19 cm −1 /(molecule.cm −2 ) in the 660–860, 860–1060, 1060–1200, and 1200–1538 cm −1 regions, respectively, by summing up the pseudoline intensity parameters. These results are observed to be significantly lower than that of the PNNL (Pacific Northwest National Laboratory) cross-sections obtained at low resolution. The pseudolines are electronically compiled in the HITRAN database format, which can be readily integrated with existing radiative transfer calculations. The measured cross-sections represented by the pseudolines could provide critical laboratory input in search of elusive species that might be captured in the Cassini/CIRS and the JWST/MIRI spectral observations. Graphic abstract: An overview of pure (in green) and N2 -mixture spectra (in magenta) of n-C4 H10 obtained at 278 K. A few representative band centers from trans and gauche conformers are identified with a help of model predictions, where, for example, v 17 (n731) reads as v 17 band of trans butane conformer centered at 731 cm −1 . Note that the band features near 667 cm −1 is CO2 ( v 2 ) band from the sample impurity. See text for further details. Image, graphical abstract