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  • 1990-1994  (67)
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  • 1
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    Spencer, "The How and Why of a Tax on Wealth" (Book Review) (1993)
    Menasha, Wis. : Periodicals Archive Online (PAO)
    The Accounting Review. 68:2 (1993:Apr.) 434 
    Details
    ISSN: 0001-4826
    Topics: Economics
    Notes: BOOK REVIEWS, Shane Moriarity, Editor
    URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pao:&rft_dat=xri:pao:article:5030-1993-068-02-000027
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  • 2
    Electronic Resource
    Electronic Resource
    The spectroscopic and photophysical effects of the position of methyl substitution. I. 4- and 5-methylpyrimidine (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 2317-2335 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Laser-induced fluorescence excitation and dispersed fluorescence spectra of the first n–π* transition of jet-cooled 4- and 5-methylpyrimidine (4-mp and 5-mp) have been recorded and analyzed. In 5-mp, methyl substitution preserves many of the spectroscopic signatures of the unsubstituted pyrimidine molecule. Dispersed fluorescence spectra are used to assign most of the major features in the first 1000 cm−1 of the excitation spectrum. High resolution scans at the origin reveal a 0.20 cm−1 splitting of the origin arising from the 0a'1–0a1 and 1e‘–1e‘ internal rotor transitions. From this small splitting we deduce that the nearly free internal rotation of the methyl group in the ground state is carried over to the S1 state as well. In 4-methylpyrimidine, the reduction in symmetry accompanying methyl substitution (G12 to G6 ) results in allowed transitions to all in-plane fundamentals. The methyl group is seen to participate in the electronic transition to a greater degree in 4-mp than in 5-mp.We observe clear activity in both the C–CH3 stretch and C–CH3 in-plane bend in the dispersed fluorescence from the origin of 4-mp. 4-mp also differs remarkably from 5-mp in the magnitude of the barrier to methyl internal rotation in S0 and S1. By fitting the positions and intensities of internal rotor structure in ground and excited states we deduce a ground state barrier to internal rotation of V‘3=95±5 cm−1 and a best-fit excited state barrier of V3=745 cm−1, V'6=−100 cm−1. Ab initio calculations on 4-mp which reproduce both the magnitude and shape of the experimental barrier to internal rotation in the ground state. The lowest energy methyl conformation places a hydrogen atom in the plane of the ring pointing away from the nitrogen lone pair. Finally, in both molecules we observe spectroscopic signatures of vibrational state mixing in the S1 state. Density-of-states calculations on both molecules using the experimentally determined internal rotor energy levels predict a similar density of same-symmetry states in the two molecules at a given energy. Experimental evidence is presented that the small V6 barrier in 5-mp leads to modest vibration/internal rotation coupling matrix elements of ∼1 cm−1. The high V3 barrier in 4-mp is observed to give strong vibration/internal rotation coupling in the case of the 6a10(0a1) level which shifts its position by 17 cm−1 from its companion 6a10(1e) level due to interaction with an X1(3a2) vibration/internal rotation combination band.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460939
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  • 3
    Electronic Resource
    Electronic Resource
    Spectroscopy and photophysics of the 1.DELTA.u .rarw. 1.SIGMA.g+ transition of jet-cooled diacetylenes (C4H2, C4HD, and C4D2) (1992)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 96 (1992), S. 5337-5343 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100192a030
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  • 4
    Electronic Resource
    Electronic Resource
    The ultraviolet photochemistry of diacetylene: Direct detection of primary products of the metastable C4H*2 + C4H2 reaction (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 5362-5374 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The products of diacetylene's ultraviolet photochemistry over the 245–220 nm region are directly determined for the first time. At these wavelengths, the photochemistry is thought to proceed from a metastable excited state of C4H2 rather than by direct photolysis. The experimental method employs a small reaction tube attached to a pulsed nozzle. C4H2 is excited within the reaction tube where collisions of C4H*2 with C4H2 form products which are subsequently ionized by vacuum ultraviolet radiation (118 nm) in the ion source of a time-of-flight mass spectrometer. The C4H*2 + C4H2 reaction produces C6H2 (+C2H2), C8H2 (+2H,H2), and C8H3 (+H), all in good yield. An extensive set of experiments is carried out to ensure that the products observed are initial products formed by single-photon excitation of gas phase C4H2. Under certain conditions, secondary products formed by subsequent reaction of the initially formed products with C4H2 are also observed. These are dominated by C10H3 and C12H3. Thermochemical arguments are made which point to C8H3+C4H2 as the source of these secondary products. Collisional deactivation of C4H*2 from its initially excited energy (∼120 kcal/mol above the ground state) to the lower levels of the metastable state (∼74 kcal/mol) is important in determining the relative amounts of C8H2 and C8H3 products. In cases where C4H*2 undergoes extensive deactivation prior to reaction, C8H3+H products dominate. When collisional deactivation is minimized, much of the C8H3 products are formed with enough energy to subsequently dissociate further to form C8H2+2H. Mechanisms are postulated for the observed reactions and some suggestions for further work to assess the importance of these reactions in planetary atmospheres are given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464909
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  • 5
    Electronic Resource
    Electronic Resource
    The spectroscopic and photophysical effects of the position of methyl substitution. II. 2-methylpyrimidine (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 1667-1675 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Laser-induced fluorescence excitation and dispersed fluorescence spectra of the first n–π* transition of jet-cooled 2-methylpyrimidine have been recorded and analyzed. This work extends our earlier study of the spectroscopic and photophysical effects of methyl substitution in 4- and 5-methylpyrimidine. An unusual Fermi resonance involving the 6an0 progression forms the focus of the present study. The 6a10 vibronic transition is observed to be split into a triad of transitions. Dispersed fluorescence spectra are used to identify the dark background state responsible for the Fermi resonance coupling as the 16b1(3a''2) vibration/internal rotation combination level. This level is selectively coupled by symmetry constraints to 6a1(0a1), leaving the 6a1(1e‘) level unperturbed. The positions and intensities of the triad of peaks in the excitation spectrum allow a quantitative determination of the 6a1(0a'1)↔16b1(3a2) coupling matrix element of V=4.1 cm−1. This vibration/internal rotation Fermi resonance is thus typical of the new types of routes to vibrational state mixing which are opened by methyl substitution. Higher members of the 6an0 progression are also involved in Fermi resonance mixing. However, in addition, these levels experience weaker, less state-specific coupling to a bath of same-symmetry states at that energy. The excitation spectrum provides an estimate of the average coupling matrix element of this second tier coupling of ∼1 cm−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462121
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  • 6
    Electronic Resource
    Electronic Resource
    Evidence for photochemical control of ozone concentrations in unpolluted marine air (1992)
    [s.l.] : Nature Publishing Group
    Nature 360 (1992), S. 446-449 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Ozone is both made and destroyed by photochemical reactions in the troposphere, the balance depending on the availability of nitrogen oxides and other gases, particularly hydrocarbons and carbon monoxide. Formation of ozone occurs through photolysis of nitrogen dioxide (formed via oxidation of ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/360446a0
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  • 7
    Electronic Resource
    Electronic Resource
    A time series for carbonyl sulfide in the northern hemisphere (1992)
    Springer
    Journal of atmospheric chemistry 14 (1992), S. 527-534 
    Details
    ISSN: 1573-0662
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The variation of OCS in the northern hemisphere for the period 1977–1991 was investigated by grouping all measurements made by our research group for that period. The data set contained 1066 measurements made in the northern hemisphere over a longitude range of 52 E to 155 W and a latitude range of 10 N to 85 N. About 50% of the measurements were made from aircraft. The overall data set had a mean of 512 parts per trillion by volume (pptv) and a standard deviation of 119 pptv. The data obtained from aircraft had a mean of 514 pptv and a standard deviation of 64 pptv. A study of the time series constructed from the data set and several subsets indicate that the change in global OCS with time is between −1.5 and 1.5 parts per trillion per year at the 95% confidence level. The data had no seasonal dependence within the precision of the data set.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00115256
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  • 8
    Electronic Resource
    Electronic Resource
    Determination of trace aqueous dimethylsulfoxide concentrations by isotope dilution gas chromatography/mass spectrometry: Application to rain and sea water (1992)
    Springer
    Journal of atmospheric chemistry 14 (1992), S. 53-60 
    Details
    ISSN: 1573-0662
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract A method has been developed for determining trace quantities of dimethyl sulfoxide (DMSO) in aqueous solutions using isotope dilution gas chromatography/mass spectrometry. The method consisted of first reducing DMSO to dimethyl sulfide (DMS), followed by purge and trap preconcentration of DMS. The concentration of DMSO was determined from the signal ratio obtained for the parent ions of DMS and d6-DMS, and the known aqueous concentration of d6-DMSO. The precision of this method was determined to be ± 2.9 %, based on replicate DMSO determinations of a test solution prepared by adding isotopically unenriched (h6-DMSO) to distilled water. The detection limit was 0.010 nmoles/L for the sampling conditions used in this study. This method was applied to the determination of DMSO concentrations in both rain and sea water. The concentration of DMSO in rain was found to be in the range of 2–4 nmoles/L for samples collected at an inland location (Phila, PA) and 8–11 nmoles/L for samples collected at a coastal location (Lewes, DE). Determination of DMSO in sea water required special sample preparation steps to eliminate positive interferences. A depth profile of DMS, DMSO, and dimethyl sulfoniopropionate (DMSP) concentrations is reported for sea water collected off the coast of Ocean City, Md, in August, 1990
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00115222
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  • 9
    Electronic Resource
    Electronic Resource
    Determination of part-per-trillion levels of atmospheric dimethyl sulfide by isotope dilution gas chromatography/mass spectrometry (1990)
    Springer
    Journal of atmospheric chemistry 11 (1990), S. 299-308 
    Details
    ISSN: 1573-0662
    Keywords: Dimethyl sulfide ; isotope dilution ; gas chromatography ; mass spectrometry ; troposphere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Stable isotopic dilution was applied to the determination of dimethyl sulfide (DMS) in ambient air at the low part-per-trillion by volume (pptrv) levels. Perdeuterated DMS was used as an internal standard in the gas chromatography/mass spectrometry determination. The isotopically labelled internal standard provided insensitivity to possible losses of DMS in sampling and analysis. The lower limit of detection (LLD) was 1 pptrv with a sample acquisition time of 2 min.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00053779
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  • 10
    Electronic Resource
    Electronic Resource
    Grab sampling for the determination of sulfur dioxide and dimethyl sulfide in air by isotope dilution gas chromatography/mass spectrometry (1993)
    Springer
    Journal of atmospheric chemistry 16 (1993), S. 23-30 
    Details
    ISSN: 1573-0662
    Keywords: Dimethyl sulfide ; sulfur dioxide ; isotope dilution ; gas chromatography ; mass spectrometry ; grab sampling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Developments allowing the direct determination of sulfur dioxide and dimethyl sulfide in grab samples by gas chromatography/mass spectrometry with isotopically labeled standards (GC/MS/ILS) are reported. Isotopomers of DMS and SO2 are used as internal standards. Spiked air samples are dried to a dew point of 〈−60 °C and trapped cryogenically in loops of Teflon tubing. Sealed samples are transported to the laboratory under liquid nitrogen and later subjected to GC/MS analysis. Holding times of up to one month do not result in significant sample loss. For samples collected in a clean marine environment, concentrations of SO2 and DMS greater than 5 and 8 pptv, respectively, are significantly different from blanks at the 95% confidence level. Average measurement precision derived from a propagation of errors are 9% for SO2 and 42% for DMS at concentrations from 5–15 pptv. Improvements are outlined which should provide sensitivity and precision comparable to that of on-site GC/MS. The technique will allow increased flexibility for the determination of trace sulfur species in the field under conditions where deployment of a mass spectrometer is not possible.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00696621
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