Work

Optical Constants of Photochemical Haze Analogs in N 2 –CH 4 –CO Atmospheres from 0.4 to 28.6 μ m

Year: 2026

Type: article

Abstract: Photochemical hazes play an important role in shaping the spectra and radiative balance of N 2 -dominated planetary atmospheres. We present newly acquired Fourier transform infrared (FTIR) and retrieved optical constants ( N = n + ik ) of laboratory-generated haze analogs from N 2 /CH 4 and N 2 /CH 4 /CO gas mixtures under plasma discharge conditions. The retrievals use particle densities newly measured for the CH 4 series and previously published particle densities for the CO series. The experiments systematically explored CH 4 concentrations from 0.5% to 10% and CO concentrations from 0% to 5% with fixed 5% CH 4 . Using measured particle densities together with the Beer–Lambert law and the subtractive Kramers–Kronig (SKK) relation, we derived optical constants over the 350–25,000 cm −1 (0.4–28.6 μ m) spectral range, with the 0.4–25 μ m results presented in the main text. The infrared spectra reveal prominent absorption features associated with hydrocarbon-, nitrogen-, and oxygen-bearing functional groups. Increasing CH 4 abundance enhances aliphatic hydrocarbon features and corresponds to decreasing particle density, whereas increasing CO abundance promotes oxygen incorporation, broader mid-infrared absorptions, and higher particle density. The derived k spectra exhibit strong absorptions near ∼3 μ m, ∼4.6 μ m, and ∼6–10 μ m, while the real refractive index n generally ranges from ∼1.2 to 1.7. The controlled CH 4 and CO series establish composition-dependent variations in haze optical properties. A benchmark comparison among Titan-, Pluto-, and Triton-like haze analogs then uses these experimentally identified trends to interpret the optical differences among N 2 -dominated planetary haze compositions. The density and optical constants provide laboratory constraints for atmospheric radiative transfer models and for interpreting planetary and exoplanetary spectra from spacecraft and telescopes.

Source: The Astrophysical Journal Supplement Series

DOI: 10.3847/1538-4365/aeaffe