Optical Constants of Photochemical Haze Analogs in N2-CH4-CO Atmospheres from 0.4 to 28.6 μm
Abstract
Photochemical hazes play an important role in shaping the spectra and radiative balance of N2-dominated planetary atmospheres. We present newly acquired FTIR and retrieved optical constants (N=n+ik) of laboratory-generated haze analogs from N2/CH4 and N2/CH4/CO gas mixtures under plasma discharge conditions. The retrievals use particle densities newly measured for the CH4-series and previously published particle densities for the CO-series. The experiments systematically explored CH4 concentrations from 0.5% to 10% and CO concentrations from 0% to 5% with fixed 5% CH4. Using measured particle densities together with the Beer-Lambert law and subtractive Kramers-Kronig (SKK) relation, we derived optical constants over the 350-25000 cm-1 (0.4-28.6 μm) spectral range, with the 0.4-25 μm results presented in the main text. The infrared spectra reveal prominent absorption features associated with hydrocarbon-, nitrogen-, and oxygen-bearing functional groups. Increasing CH4 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 μm, ~4.6 μm, and ~6-10 μm, while the real refractive index n generally ranges from ~1.2 to 1.7. The controlled CH4- 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 N2-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
@misc{yang2026optical,
title = {{Optical Constants of Photochemical Haze Analogs in N2-CH4-CO Atmospheres from 0.4 to 28.6 μm}},
author = {Zhengbo Yang and Chao He and Haixin Li and Sai Wang and Xiao'ou Luo and Yu Liu and Sarah M. Hörst},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.22982},
eprint = {2609.22982},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.22982},
note = {CC BY-SA 4.0},
}
RIS
TY - UNPB
TI - Optical Constants of Photochemical Haze Analogs in N2-CH4-CO Atmospheres from 0.4 to 28.6 μm
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 - 2026/09/19
PB - arXiv
DO - 10.48550/arxiv.2609.22982
UR - https://arxiv.org/abs/2609.22982
AB - Photochemical hazes play an important role in shaping the spectra and radiative balance of N2-dominated planetary atmospheres. We present newly acquired FTIR and retrieved optical constants (N=n+ik) of laboratory-generated haze analogs from N2/CH4 and N2/CH4/CO gas mixtures under plasma discharge conditions. The retrievals use particle densities newly measured for the CH4-series and previously published particle densities for the CO-series. The experiments systematically explored CH4 concentrations from 0.5% to 10% and CO concentrations from 0% to 5% with fixed 5% CH4. Using measured particle densities together with the Beer-Lambert law and subtractive Kramers-Kronig (SKK) relation, we derived optical constants over the 350-25000 cm-1 (0.4-28.6 μm) spectral range, with the 0.4-25 μm results presented in the main text. The infrared spectra reveal prominent absorption features associated with hydrocarbon-, nitrogen-, and oxygen-bearing functional groups. Increasing CH4 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 μm, ~4.6 μm, and ~6-10 μm, while the real refractive index n generally ranges from ~1.2 to 1.7. The controlled CH4- 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 N2-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.
ER -