Dissertation/Thesis Abstract

Towards a Chemical Taxonomy of Comets: Infrared Spectroscopic Methods for Quantitative Measurements of Cometary Water (With an Independent Chapter on Mars Polar Science)
by Bonev, Boncho P., Ph.D., The University of Toledo, 2005, 323; 10836001
Abstract (Summary)

While comets are often grouped according to their orbital properties, it is increasingly clear that individual groupings likely contain objects formed in diverse regions of the proto-planetary disk. In recent years the emergence of accurate abundance measurements for volatile native constituents has begun to permit a taxonomic classification reflecting the chemical diversity in the composition of the cometary nucleus. The baseline of this taxonomy is the measured production of H2O – the dominant volatile species in comets, which controls the sublimation of other molecules within 2-3 astronomical units from the Sun. Accurate quantitative production rates of water are critical because they provide the "baseline" for comparison with organic species; their simultaneous measurement eliminates many sources of systematic error.

This project explores two infrared spectroscopic methods to quantify H2O production in comets. The first method is based on H2 O non-resonance fluorescence and is well established. The present work improves its application. The initial development of the second method, based on infrared emission from an excited dissociation fragment (OH), is the main original contribution of this work. In addition to obtaining H2O production rates, the newly developed formalism provides insights about the process of H2O photo-dissociation, in particular – the relative populations of vibrationally- and highly rotationally-excited states of OH produced by water photolysis.

The five principal contributions of this thesis are: (1) Development of a second method to measure H2O production at infrared wavelengths, including evaluation of its potential limitations and definition of a future program to further validate it; (2) Observations of the end-product distribution of H2O photolysis under natural conditions that differ greatly from studies done in terrestrial laboratories; (3) Measurement of H2 O spin temperatures in two comets with realistic treatment of uncertainties; (4) Derivation of reliable water production rates from directly sampled non-resonance fluorescent H2O emission in two comets. These production rates provide a solid baseline for describing the volatile chemistry of these comets; and (5) Reliable measurements of the H2O integrated column abundance in comet 9P/Tempel-1, during the observing campaign supporting the NASA's Deep Impact mission.

Indexing (document details)
Advisor: James, Philip
School: The University of Toledo
Department: Physics
School Location: United States -- Ohio
Source: DAI-B 79/10(E), Dissertation Abstracts International
Subjects: Physics
Keywords: Chemical taxonomy, Comets, H2o fluorescence, Infrared, Molecular spectroscopy, Solar system
Publication Number: 10836001
ISBN: 9780355971859
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