Mathematics – Logic
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995phdt........17m&link_type=abstract
Thesis (PH.D.)--STANFORD UNIVERSITY, 1995.Source: Dissertation Abstracts International, Volume: 56-10, Section: B, page: 5508.
Mathematics
Logic
4
Chondritic Meteorites, Sapphire
Scientific paper
This thesis describes the use of two-step laser mass spectrometry (L^2MS), a combination of infrared (IR) laser desorption with resonance-enhanced multiphoton ionization (REMPI) and time-of-flight (TOF) mass spectrometry, to investigate (1) the mechanism of IR laser desorption, (2) the composition of aromatic molecules in extraterrestrial samples, and (3) the measurement of compound-specific carbon isotope ratios. First, a description of the mechanism of IR laser desorption of monolayer and submonolayer coverages of molecules adsorbed to an insulator surface is presented. The vibrational and translational energy distributions of aniline-d7 molecules desorbed from single-crystal sapphire (Al_2 O_3) are recorded using L ^2MS. The energy distributions are found to be in equilibrium with each other and with the temperature of the surface at the time of desorption. The translational and angular distributions of monolayer coverages are altered by the collisions of desorbing molecules with each other. Second, spatial and chemical analyses of the carbonaceous components in chondritic meteorites are presented. A microprobe L^2MS instrument (mu L^2MS) capable of analyzing samples with a spatial resolution of 40 mu m and zeptomole (10^{-21} mole) sensitivity is described and used to investigate polycyclic aromatic hydrocarbons (PAHs) in small particles and heterogeneous samples. PAH distributions are used to distinguish between samples from different meteorite classes, and the effects of thermal processing within a given meteorite class are observed. Sliced wafers of meteorite are found to contain an inhomogeneous distribution of PAHs. muL^2MS studies of meteorite samples are coordinated with scanning electron microscopy studies, and the abundances of aromatic compounds across the surface of a sample are consistent with gross structural features but not with elemental or mineralogical features. Third, a description of a method for performing compound-specific carbon isotope ratio analyses using REMPI followed by TOF mass spectrometry is presented. Measurements of carbon isotope ratios (delta^{13 }C) for the volatile aromatic compounds m-xylene -d10, toluene, and toluene-d8 are described. A simple procedure for deriving the abundances of ^{12 }C and 13C from the TOF spectra is presented, and delta 13C values with a precision of +/-30 parts per million are achieved. Complications caused by and corrections for detector nonlinearity and parent ion fragmentation are discussed.
Maechling Claude Ricketts
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