Laser desorption mass spectrometry of complex aromatics in meteorites, asphaltenes, and interstellar ice analogs.

摘要

Laser desorption mass spectrometry techniques were used to study complex aromatic hydrocarbons in both terrestrial and extraterrestrial materials, including carbonaceous chondrite meteorites, fossil fuel asphaltenes, and ultraviolet-irradiated interstellar ice analogs.;Laser desorption mass spectrometry (LDMS) was performed on meteoritic insoluble organic matter (IOM), which is isolated from meteorite powders by a series of chemical digestions. The LDMS analysis reveals a clear and intense envelope of evenly spaced peaks that are diagnostic of the presence of fullerenes. It is demonstrated that these fullerene peaks are produced from the IOM during the laser event. It is further found that IOM can confound traditional extraction experiments by providing a source for a false positive fullerene signal when LDMS is used as the detection technique. The implications of this false positive signal on the current reports of fullerenes in meteoritic samples are discussed in the context of this finding.;Two-step laser mass spectrometry (muL2MS) was explored as a technique to measure the molecular-mass distribution of asphaltenes. Detailed studies of relevant model compounds confirms that muL2MS suffers very little from plasma effects such as gas-phase aggregation and likely provides a slight underestimate of the asphaltene molecular-mass distribution. Petroleum asphaltenes from different geographical origins were found to have similar mass spectra, all showing a peak at every nominal mass under an envelope beginning at 200 units, peaking at 500--600 units, and extending to 1000--1500 units. Coal asphaltenes were found to be considerably lighter and less complex, showing pronounced clusters of peaks separated by 14 units under an envelope ranging from 200 to 500 Da. These results agree with measurements of asphaltenes made by other mass spectrometry and diffusion-based techniques and help establish laser-based mass spectrometry as a reliable tool for asphaltene mass-distribution measurement for the first time.;Chemical modification of the polycyclic aromatic nitrogen heterocycle (PANH) quinoline (C9H7N) in interstellar ice analogs was investigated by high-performance liquid chromatography, muL2 MS, and a nanoscale liquid chromatography-electrospray ionization mass spectrometry technique. The ultraviolet-radiation-exposed ices showed a variety of side-group additions to the aromatic structure as the dominant reaction pathway, including addition of hydrogen (-H), hydroxy (-OH), ketone (-C=0), carboxylic (-COOH), methyl (-CH3), and methoxy (-OCH 3) substituents, with the suite of hydroxyquinolines being the dominant reaction pathway. Product distribution varied little over a range of parameters, including temperature, reactant ratios, and radiation dose. This work indicates that oxidation of PANHs could occur in icy extraterrestrial environments and suggests that a search for such compounds in carbonaceous meteorites could illuminate the possible link between interstellar ice chemistry and meteoritic organics.