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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 36 (1985), S. 63-75 
    ISSN: 1432-0649
    Keywords: 82.50 ; 33
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The laboratory scale-up of a two-stage laser enrichment process for carbon isotopes, involving infrared multiphoton dissociation of freon-22, is described. Unmodified commercial equipment and materials were used. An initial study of the effect of fluence, laser frequency, freon-22 pressure and pressure of argon, nitrogen and trifluoromethyl chloride was made in short irradiation cells (constant fluence) in order to define optimum process parameters. The process was then scaled to higher throughput in longer cells (1–5 m) in which compensation for beam-energy depletion by absorption was made by reduction in the beam area by focussing. From the scale-up experiments, measurements of yield and enrichment of the tetrafluoroethylene product gave demonstrated production rates. These, coupled with measurements of the absorption, allowed extrapolation to production rates assuming total utilization of the available output energy. Using a 100 W TEA CO2 laser (10 J, 10 Hz) we have demonstrated production rates of 0.20 g h−1 carbon-12 at 99.99% carbon-12, 11 mg h−1 carbon-13 at 72% carbon-13 and 2 kg per annum carbon-13 at 50%. Energy absorption measurements imply a capability to produce 3 kg per annum carbon-13 at over 95% carbon-13 in a two-stage process. The apparatus was used to produce gram quantities of carbon-13 depleted freon-22 (99.99% carbon-12). A comparison of the infrared multiphoton dissociation of this material with that of natural freon-22 (1.11% carbon-13) showed that under the conditions required to give selective dissociation of13CF2HCl that12CF2HCl was excited as a result of a dominantly radiative interaction and that collisional transfer from13CF2HCl molecules played a minor role.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0649
    Keywords: 82.50 ; 33
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract There is a general agreement that efficient infrafed laser induced separation of carbon isotopes requires a two-stage process. An efficient first stage 1%→50%13C enrichment was shown by Gauthier et al. [1] to be feasible and competitive with conventional technology. In this work, second-stage CO2 laser enrichment of equimolar mixtures of12CHClF2 and13CHClF2 has been demonstrated yielding tetrafluoroethylene containing 95% or 99%13C. Forward enrichment by selective decomposition of the13CHClF2 fraction was very efficient, absorbing only 6 and 16 eV, respectively, per carbon atom produced at 95% and 99%13C content.
    Type of Medium: Electronic Resource
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  • 3
    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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