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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 28 (1982), S. 43-50 
    ISSN: 1432-0649
    Keywords: 82.50, 33
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report the isotopically selective decomposition of chlorodifluoromethane. Chlorodifluoromethane is used industrially in high volume for the production of tetrafluoroethylene and its polymers; thereby it is an attractive working substrate for a medium scale isotope separation process, both in terms of its price and availability. We have studied the infrared multiphoton decomposition of carbon-13 substituted chlorodifluoromethane molecules present at their natural abundance (1.11%). A well defined CO2 laser pulse (80 ns FWHM) was used and both the yield of carbon-13 enriched product and the net absorption of laser radiation were measured. These measurements were made as a function of substrate pressure (10-800 Torr), CO2 laser line (9P 12–9P 32) and fluence (2–8 J cm−2) and were used to determine the energy expenditure per carbon atom produced (ε) at specified product carbon-13 content in the range 30%–96%. The results of these parametric studies were interpreted in terms of the kinetics of multiphoton absorption and dissociation, and allowed an initial optimization of the experimental conditions to minimize ε. Optimum results were obtained at 1046.9 cm−1, 69 cm−1 to the red of the12CHClF2 v 9 band center. Irradiation of 100 Torr of chlorodifluoromethane at 3.5 J cm−2 gave tetrafluoroethylene containing 50% carbon-13 for an absorption of 140 photons (0.017 keV) per carbon atom produced. This efficiency compares favourably with existing carbon-13 enrichment technologies and would require an absorption pathlength of only 2 m to absorb half the incident photons.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Although nitrogen inversion in unsubstituted aziridines has been shown by 1H NMR, it was only possible to study quantitatively the distribution of both invertomers and determine the thermodynamic parameters by a systematic high field NMR study (CAMECA 250 MHz). Thermodynamic parameters have been determined for 32 compounds. In C-aryl aziridines, the steric hindrance of the aromatic group and its variation with other aziridine ring substituents can be studied. These observations are in agreement with a conjugation phenomenon between the aromatic system and the aziridine ring.
    Notes: Bien que le phénomène d'inversion de l'azote dans les aziridines secondaires ait pu être mis en évidence par RMN 1H, seule une étude systématique à 250 MHz a permis d'étudier quantitativement la répartion des deux invertomères et ainsi, de déterminer les paramètres thermodynamiques liés à l'équilibre conformationnel. Ces paramètres ont été déterminés pour 32 composés. Dans les aziridines C-phénylées, une variation de l'encombrement du groupement aromatique en fonction des autres substituants du cycle aziridine peut être mis en évidence. Ces observations prouvent l'existence d'un phénomène de conjugaison entre système aromatique et petit cycle. phénomène préalablement mis en évidence par effet Faraday.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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