Optical Constants of Photochemical Haze Analogs in N ₂ –CH ₄ –CO Atmospheres from 0.4 to 28.6 μ m
- 1University of Science and Technology of China
- 2Johns Hopkins University
- 3Space Telescope Science Institute
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.
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BibTeX
@article{yang2026optical,
title = {{Optical Constants of Photochemical Haze Analogs in N ₂ –CH ₄ –CO Atmospheres from 0.4 to 28.6 μ m}},
author = {Zhengbo Yang and Chao He and Haixin Li and Sai Wang and Xiao’ou Luo and Yu Liu and Sarah M. Hörst},
journal = {The Astrophysical Journal Supplement Series},
year = {2026},
month = nov,
doi = {10.3847/1538-4365/aeaffe},
url = {https://iopscience.iop.org/article/10.3847/1538-4365/aeaffe},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Optical Constants of Photochemical Haze Analogs in N ₂ –CH ₄ –CO Atmospheres from 0.4 to 28.6 μ m
AU - Zhengbo Yang
AU - Chao He
AU - Haixin Li
AU - Sai Wang
AU - Xiao’ou Luo
AU - Yu Liu
AU - Sarah M. Hörst
PY - 2026
DA - 2026/11/04
JO - The Astrophysical Journal Supplement Series
DO - 10.3847/1538-4365/aeaffe
UR - https://iopscience.iop.org/article/10.3847/1538-4365/aeaffe
AB - 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.
SN - 0067-0049
SN - 1538-4365
ER -