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UV and IR spectroscopy of polyynes: applications
to planetary atmospheres and to the ISM
Francois Shindo
Atomic and Molecular Physics Division
Harvard-Smithsonian Center for Astrophysics
Monday, November 17, 2003
11:45, Pratt Conference Room
Harvard-Smithsonian Center for Astrophysics
Abstract:
Solid organic matter is observed through specific spectral signatures
in proto-planetary nebulae, in planetary atmospheres and in the
interstellar medium. One chemical pathway from gaseous phase
to solid phase could be the molecules called polyynes (C_2nH_2
and HC_2nCN), polymerization of which would lead to the production
of macromolecules. However, the detection of these compounds
and the determination of their abundances are limited by a lack
of gaseous spectroscopic information for n>3, due to high
instability in laboratory conditions. I report here my spectral
study of two polyynes, namely C6H2 and C8H2, in the spectral
domains 180-320 nm (UV) and 220-4300 cm-1 (IR). IR measurments
at room temperature allow calibration of synthetic spectra before
application to low T environments. However, calculations are
limited since high-resolution spectra of C6H2 reveal complex
rotation-vibration structures arising from hot bands. Finally,
the present results lead to constraints on! the maximum mole
fraction of these molecules in Titan atmosphere (Saturn's satellite),
to the possible first extraterrestrial observation of C8H2 (in
the proto-planetary nebula CRL 618), and to an explanation of
the differences of polyynes abundances in Titan and CRL 618 through
a basic photochemical model.
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