C-H Hot Bands in the Near-IR Emission Spectra of the Leonids

Details C-H Hot Bands in the Near-IR Emission Spectra of the Leonids C-H Hot Bands in the Near-IR Emission Spectra of the Leonids

Nov 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002nla..work..245f&link_type=abstract

NASA Laboratory Astrophysics Workshop, held May 1-3 2002 at NASA Ames Research Center, Moffett Field, CA 94035-1000. Publisher:

Astronomy and Astrophysics

Astrophysics

Scientific paper

The reported infrared (IR) emission spectra from 1999 Leonid fireballs show a 3.4μm C-H emission band and unidentified bands at longer wavelengths. Upon atmospheric entry, the Leonid meteorites were flash-heated to temperatures around 2400K, which would destroy any organics on the surface of the meteorite grains. We propose that the vcH emission hand in the Leonid emission spectra arises from matrix-embedded Cn-H-O entities that are protected from instant pyrolysis. Our model is based on IR absorption vcH bands, which we observed in laboratory-grown MgO and natural olivine single crystals, where they arise from Cn-H-O units imbedded in the mineral matrix, indicative of aliphatic -CH2- and -CR3 organics. Instead of being pyrolyzed, the Cn-H-O entities in the Leonid trails become vibrationally excited to higher levels n = 1, 2, 3 etc. During de- excitation they emit at 3.4μm, due to the (0 => 1) transition, and at longer wavelengths, due to hot bands. As a first step toward verifying this hypothesis we measured the C-H vibrational manifold of hexane (C6H14). The calculated positions of the (2 => 1), (3 => 2), and possibly (4 => 3) hot bands agree with the Leonid emission bands at 3.5, 3.8 and 4.1μm.

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