Computer Science
Scientific paper
Jan 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996phdt.........7h&link_type=abstract
Thesis (PH.D.)--MICHIGAN STATE UNIVERSITY, 1996.Source: Dissertation Abstracts International, Volume: 57-05, Section: B, page: 3
Computer Science
Vibrational Spectroscopy, Matrix Isolation, Carbon Disulphide Cation, Tropylium Cation
Scientific paper
We have proposed instrumentation for the accumulation and infrared spectroscopic characterization of mass-selected ions using matrix-isolation techniques. In the method, both mass-selected cations and anions can be deposited with an inert host on a window held at low temperature for subsequent spectroscopic examination. Our ultimate goal is to couple mass-selective ion sources that produce sufficient numbers of both positively- and negatively-charged species with the appropriate matrix-isolation hardware to allow the determination of ionic structures by vibrational spectroscopy. Upon completion of an ion source that produces suitable currents of mass-selected CF_3 ^+, we found that these cations can be trapped in a matrix, allowing for infrared measurements to be carried out without the concurrent deposition of negatively-charged species. We have also discovered that the addition of carbon dioxide to the neon matrix gas during deposition of a mass-selected cation beam results in detectable quantities of CO_2^{-.}. It is shown that negative charge formation is strongly dependent on the temperature of the metallic surfaces surrounding the matrix window and the presence of condensable gases on these surfaces. Vibrational spectroscopic characterization of neon matrices in which mass-selected CS_2 ^{+.} was deposited reveals absorptions due to CS_2^{+.} and CS_2^{-.}. A comparison of the results from these investigations with those from CO_2^{+.} studies reveal several interesting aspects of the matrix deposition process. For this set of mass-selected cations, no "matrix chemistry" products, such as the production of H_2O^{+.} through charge exchange with the mass-selected cation, and no fragmentation products of the mass-selected cations are observed. It is also determined that CO_2 is a better matrix additive than CS_2 for counterion generation. The results from these experiments are used to interpret the data from investigations of mass-selected organic cations such as the tropylium (C_7H_7^+) cation. We also report controlled annealing studies of the matrices in which clustering of ionic species with neutral molecules is observed.
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