Computer Science
Scientific paper
Aug 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997phdt.........4w&link_type=abstract
Thesis (PHD). UNIVERSITY OF FLORIDA , Source DAI-B 58/07, p. 3661, Jan 1998, 123 pages.
Computer Science
Interstellar Space, Polycyclic Aromatic Hydrocarbons, Unidentified Interstellar Emissions
Scientific paper
Many of the molecules purported to exist in interstellar space can only be generated in high temperature processes or are ions that are difficult to produce at high enough concentrations for spectroscopic analysis. The molecules investigated in this study, specifically, were polycyclic aromatic hydrocarbon (PAH) ions, carbon chain water complexes and carbon chain anions. PAHs are the proposed carriers of the unidentified interstellar (UIR) emission. The infrared investigation of pentacene and tetracene ions was pursued to provide data concerning the possibility that PAH cations were the source of the UIR emission. In this study, infrared features corresponding to both cation and anions for both molecules were observed for the first time. The most intense features for the neutral molecules were the CH out-of-plane wagging modes while the most intense cationic and anionic features were in the CC stretch and CH bending regions. The relative intensities from theoretical calculations were in reasonable agreement with experimental values with the exception of an overestimation for the intensities of the CH stretch in both neutral pentacene and tetracene. Carbon chain water complexes are very weakly bound species that are observed when graphite is vaporized at low power. The infrared features increase in intensity and new ones appear after annealing a matrix containing carbon chain molecules and H2O. The current study involved assignment of infrared features at 1959.4 and 2014.4 cm-1 to C6ċ H2O and C9ċ H2O, respectively. Assignments were based on the fact that both bands increased relative to the C9 and C6 bands when the concentration of H2O increased. The band assignments were further justified by a 12,13C study for C6/cdotH2O and the agreement of the theoretical shift, relative to the asymmetric stretch band of C9, for C9ċ H2O. In addition a new feature at 1550.4 cm-1 was tentatively assigned to C4ċ H2O. Finally, an isotopic study of a feature at 1721.8 cm-1 confirmed the assignment of the band to the asymmetric stretching mode of linear C3-. The calculated isotopic shifts are in very good agreement. In addition, calculations based on the GF matrix method confirmed a linear structure for C3- in an Ar matrix.
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