N2- and (H2+He)-broadened cross sections of benzene (C6H6) in the 7–15 µm region for the Titan and jovian atmospheres

Abstract

In support of atmospheric remote sensing of Titan and jovian planets, we measured absorption cross sections of benzene (C6H6) in the 7–15µm region at temperatures between 235K and 297K. For this, high-resolution laboratory spectra of C6H6 were obtained using two cold cells (80cm and 2.07cm path length) configured to a high resolution Fourier-transform infrared (FT-IR) spectrometer, Bruker IFS-125HR, at the Jet Propulsion Laboratory (JPL). The spectrum sets include 15 pure and 15 N2-broadened benzene spectra in the 630–1534cm−1 region, along with four additional spectra broadened by an H2(85%) and He(15%) gas mixture for the 630–740cm-1 region. From these spectra, temperature dependent benzene cross sections were obtained for gas phase benzene in the presence of N2 and (H2+He) at ambient pressures and temperatures down to 235K.In addition, we generated two independent sets of pseudolines: one of N2-broadened benzene for Titan and the other of (H2+He)-broadened benzene for jovian planets. It is shown that the benzene pseudolines can reproduce the observed features to ∼ 5% in transmittance, including the continuum-like absorption formed by numerous overlapping weak and hot band transitions. Based on the pseudoline parameters, the integrated band intensities at 296K for the three strongest bands in the region were measured to be 177.0(73), 14.0(10), 27.2(9)×10−17cm−1/(molecule·cm−2) in the region of v4 at 674cm−1, v14 at 1038.267, and v13 at 1483.985cm−1, respectively, from the combined set of pure and N2-broadened benzene spectra. For the (H2+He) mixture-broadened benzene spectra, the integrated band intensity for v4 band in the 630–735cm−1 region was measured to be 168.8(17)×10−17cm−1/(molecule·cm−2) at 296K, which is in agreement with the intensity derived from the N2-broadened benzene spectra within the combined measurement uncertainties. The results from this work show an excellent agreement (2%) with one of the latest experimental studies by Rinsland et al. (2008). Furthermore, additional characteristics carried by the pseudolines approach are discussed. Finally, we provide the two sets of pseudo line list (PLL) as electronic supplements.