Laser microprobe studies of complex aromatic molecules on meteorites and interplanetary dust.

摘要

The moon is the only other body in the Cosmos that we as humans have visited and returned from with samples. In this light, it is perhaps remarkable to realize that samples of comets, asteroids, Mars, and even dust that permeates the interstellar medium are already available for us to study here on Earth. These samples are brought to us in the constant influx of meteorites and interplanetary dust to our planet, amounting to some 40 million kg per year. Unfortunately, only the tiniest fraction of this material can ever be recovered. Consequently, ultrasensitive microanalytical techniques are essential if we are to ever understand the role this matter has played in the origin and evolution of our Solar System.; By combining focused laser-assisted thermal desorption with ultra-sensitive laser photo-ionization methods, we have been able to design and construct a microprobe laser desorption/laser ionization mass spectrometer {dollar}rm(mu Lsp2MS){dollar} that can spatially resolve the distribution of organic molecules on complex surfaces and small particles. This {dollar}rmmu Lsp2MS{dollar} instrument is currently the most sensitive analytical instrument known for the in situ detection of polycyclic aromatic hydrocarbons (PAHs), with detection limits at the few thousand molecule level, and a spatial resolution of 40 {dollar}mu{dollar}m.; We have used the {dollar}rmmu Lsp2MS{dollar} instrument to investigate the nature and distribution of aromatic (benzenzoid-containing) hydrocarbons in primitive extraterrestrial materials with the aim of addressing the origin and abiotic evolution of organic molecules both within our Solar System and the interstellar medium beyond. Specifically, the work presented in this thesis focuses on three types of extraterrestrial material: (1) the matrix of chondritic meteorites, (2) interplanetary dust particles and (3) interstellar grains. We have been able to detect the presence of organic species in materials previously impossible owing to limited sample sizes and trace abundances. Because our technique is essentially nondestructive from a mineralogical viewpoint we have been committed to collaborative efforts in which we have coordinated our analyses with complementary techniques, including scanning electron microscopy, transmission electron microscopy, micro-Raman and infrared spectroscopy, and ion microprobe analysis.