Study On Spectroscopy Of Organic Matter In Carbonaceous Chondrites

Carbonaceous chondrites(CCs)are important materials for understanding the early evolution of the solar system and the transportation process of extraterrestrial organic matter.The source of their parent bodies,C-type asteroids,are important objects for deep space exploration.Spectral analysis of carbonaceous chondrites can establish the relationship between them and their parent asteroids,which helps to determine the surface composition of the asteroid.This paper analyzes the visible-far infrared reflectance spectra of 6 CM2 carbonaceous chondrites,and compares them with a series of different types of coals(earth analogues of organic matter contained in carbonaceous chondrites).Combining their chemical composition information,the relationship between infrared spectra and organic components can be derived.In addition,the effects of different heating times and temperatures on the spectrum of coals are also studied.The results show that absorptions in coal spectrum are strongly related to elemental H/C ratio when the H/C>0.55.In the 3-4 μm region,the CM2 meteorites have obvious aliphatic CH2 and CH3 absorptions and weak aromatic C=C and C=O absorption bands in the 5-6.5 μm region.Compared with coals spectrum,carbonaceous chondrites lack the 3.28 μm aromatic CH absorption.The infrared spectrum absorption indicated that the organic components of CM2 carbonaceous chondrite contain both aliphatic and aromatic compounds.The reason for the unobvious spectral characteristics in the 3.28 μm may be the overlapping absorption of hydrous minerals OH or the strong absorption of opaque minerals,resulting in low overall reflectivity in these bands and weak aromatic absorption characteristics.As the heating time increased,the organic group absorption at 3.28,3.38,3.41,3.48 and 5-6.5 μm decreased significantly.When the meteorite samples are heated above 400℃,the absorption of aliphatic organics at 3.38,3.41 and 3.48μm disappeared,and the absorption of aromatic organics at 5-6.5μm decreased.This may be because the high temperature destroys the chemical structure of the organic groups,resulting in the dehydrogenation of organic molecules.