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Polycyclic aromatic hydrocarbon mole...

Lee, Wei.

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Polycyclic aromatic hydrocarbon molecules of astrophysical interest.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Polycyclic aromatic hydrocarbon molecules of astrophysical interest./
Author:	Lee, Wei.
Published:	Ann Arbor : ProQuest Dissertations & Theses, : 1993,
Description:	163 p.
Notes:	Source: Dissertations Abstracts International, Volume: 56-01, Section: B.
Contained By:	Dissertations Abstracts International56-01B.
Subject:	Astrophysics. -
Online resource:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=9419292
ISBN:	9798208063552

Polycyclic aromatic hydrocarbon molecules of astrophysical interest.
Lee, Wei.

Polycyclic aromatic hydrocarbon molecules of astrophysical interest. - Ann Arbor : ProQuest Dissertations & Theses, 1993 - 163 p.

Source: Dissertations Abstracts International, Volume: 56-01, Section: B.

Thesis (Ph.D.)--The University of Alabama at Birmingham, 1993.

This research seeks to provide a more rigorous experimental foundation for the hypothesis of polycyclic aromatic hydrocarbon (PAH) molecules being a prominent constituent of the interstellar medium (ISM) by evaluating the roles they may have in contributing to the interstellar extinction curve, the diffuse interstellar absorption bands (DIBs), and the unidentified infrared (UIR) emissions. As an interstellar hydrocarbon component, complex molecules such as PAHs need also to be considered in scenarios leading to the presence of hydrocarbons in the solar nebula during formation of the solar system. The hypothesis that PAHs are responsible for the cosmic UIR bands is primarily a result of the general correlation between the UIR features and the laboratory absorption spectra of PAHs. A serious problem has been that the strong absorption features in the near-UV are not seen in the interstellar extinction curve. The first part of this research has been aimed toward removing this conflict. The experiment involved electronic absorption measurements on both neutral and cationic forms of PAH species. The pronounced decrease in the strength of the near-UV absorption bands of the neutral species upon ionization by gamma radiation indicates that PAHs, which are expected to be ionized in the general ISM and still to produce the UIR emissions, would not exhibit near-UV features from the bluest DIB at 4428 A to the UV extinction bump at 2175 A. In considering the possible contribution of interstellar PAHs to the hydrocarbon component in carbonaceous chondrites and interplanetary dust particles (IDPs), the mid-IR spectrum of a film-like deposit produced through plasma discharge of a gaseous mixture of hydrogen and the simplest PAH, naphthalene, has been obtained. This experiment that has evidently resulted in the synthesis of a laboratory analog for the hydrocarbon component of the alkane-predominant Murchison meteorite suggests that the hydrocarbon material originated as PAHs formed in the atmospheres of carbon stars during their later stages of stellar evolution. It also implies that the pathway from those formation sites, to the interstellar space where they become enriched with deuterium in dark clouds, and to incorporation into the parent bodies of meorites and IDPs probably involved hydrogenation of PAHs into alkanes in plasma of the solar nebula or in H scII regions prior to the solar nebula.

ISBN: 9798208063552Subjects--Topical Terms:

535904
Astrophysics.
Subjects--Index Terms:

infrared emissions

Polycyclic aromatic hydrocarbon molecules of astrophysical interest.
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245 1 0 $a Polycyclic aromatic hydrocarbon molecules of astrophysical interest.
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300 $a 163 p.
500 $a Source: Dissertations Abstracts International, Volume: 56-01, Section: B.
500 $a Publisher info.: Dissertation/Thesis.
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502 $a Thesis (Ph.D.)--The University of Alabama at Birmingham, 1993.
520 $a This research seeks to provide a more rigorous experimental foundation for the hypothesis of polycyclic aromatic hydrocarbon (PAH) molecules being a prominent constituent of the interstellar medium (ISM) by evaluating the roles they may have in contributing to the interstellar extinction curve, the diffuse interstellar absorption bands (DIBs), and the unidentified infrared (UIR) emissions. As an interstellar hydrocarbon component, complex molecules such as PAHs need also to be considered in scenarios leading to the presence of hydrocarbons in the solar nebula during formation of the solar system. The hypothesis that PAHs are responsible for the cosmic UIR bands is primarily a result of the general correlation between the UIR features and the laboratory absorption spectra of PAHs. A serious problem has been that the strong absorption features in the near-UV are not seen in the interstellar extinction curve. The first part of this research has been aimed toward removing this conflict. The experiment involved electronic absorption measurements on both neutral and cationic forms of PAH species. The pronounced decrease in the strength of the near-UV absorption bands of the neutral species upon ionization by gamma radiation indicates that PAHs, which are expected to be ionized in the general ISM and still to produce the UIR emissions, would not exhibit near-UV features from the bluest DIB at 4428 A to the UV extinction bump at 2175 A. In considering the possible contribution of interstellar PAHs to the hydrocarbon component in carbonaceous chondrites and interplanetary dust particles (IDPs), the mid-IR spectrum of a film-like deposit produced through plasma discharge of a gaseous mixture of hydrogen and the simplest PAH, naphthalene, has been obtained. This experiment that has evidently resulted in the synthesis of a laboratory analog for the hydrocarbon component of the alkane-predominant Murchison meteorite suggests that the hydrocarbon material originated as PAHs formed in the atmospheres of carbon stars during their later stages of stellar evolution. It also implies that the pathway from those formation sites, to the interstellar space where they become enriched with deuterium in dark clouds, and to incorporation into the parent bodies of meorites and IDPs probably involved hydrogenation of PAHs into alkanes in plasma of the solar nebula or in H scII regions prior to the solar nebula.
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