The relative rates of hydrogen and deuterium abstraction by chlorine atoms from H2–D2, CH4–CD4, and C2H6–C2D6 in direct competition have been studied by a mass spectrometer technique permitting direct determinations of rates. The pair CHCl3–CDCl3 was investigated by a substitution—addition competition with C2Cl4. Data were obtained between 300° and 475°K, and values of kH/kD ranged between 3.64 and 10.9 for CH4/CD4, 2.37 to 2.69 for C2H6/C2D6, 1.58 to 2.26 for CHCl3/CDCl3, and 4.7 to 8.9 for H2/D2. For the family of reactions involving C–H–Cl, an extensive series of model calculations were made by the ``bond-energy—bond-order'' method. The expected variation of activation energy with heat of reaction was computed and compared with experiment. The expected variation of kinetic isotope effect with both temperature and heat of reaction was computed for a range of conditions much wider than these experiments. Simple activated complex theory predicts several strong trends of kinetic isotope effect with heat of reaction. The data, in a general semiquantitative way, follow these predicted trends, but in terms of fine details the data do not fit the theoretical lines. In view of the known simplifications in activated complex theory, this agreement with broad trends is all that anyone should expect.
Herrn Professor Dr. R i c h a r d Kuhn zurn 60. Geburtstag gewidrnetDie Photochlorierung von Gemischen aus C2CI4 einerseits und CH4, CH3C1, CHzC12 oder CHCI, anderseits, sowie die Photochlorierung von CH4, CH3CI und CH2Cl2 wurden untersucht; die drei letztgenannten Reaktionen sind ebenfalls einer Untersuchung von Gemischen aquivalent, da die Reaktionsprodukte einen starken EinfluB auf den Redktionsverlauf haben. Es werden kinetische Gleichungen abgeleitet; ferner wird eine Reaktionszeit definiert (im wesentlichen das Inverse einer Reaktionsgeschwindigkeitskonstanten) : die Reaktionszeit in einem Gemisch ist gleich der Summe der Reaktionszeiten der Komponenten. Diese kinetischen Betrachtungen gestatten es, den komplizierten Verlauf der Photochlorierung von CH4, CH3CI und CHzClz zu klaren. Unter Zuhilfenahrne einiger Literaturangdben werden so zuverllssige Werte fur etwa 40 Geschwindigkeitskonstanten elementarer Atom-und Radikalreaktionen erhalten. * ) Boursier de I'IRSIA (Institut pour I'Encouragcment de la Recherche Scientifique dans I'Industric et I'Agriculture, Bruxelles).
La constante cinttique de recombinaison des atomes de chlore avec des molkules C l z comme troisikme corps a BtB mesuree en etudiant l'addition du chlore B l'oxyde de carbone dans un intervalle de temperature compris entre 500 et WOK. Les valeurs trouvkespourlog krec sont 9.9 rt 0.5,9.85 f0.5, 9.70f0.5 en l2 sec-l respectivement B 502.4, 552.3 et 598.9OK. L'efficacitb du tktrachlorure de carbone comme troisihe corps est environ 6.5 fois plus grande que celle de Cl2, alors que SFS et A n'ont pas d'efficacitk mesurable avec cette mkthode dont la sensibilitk est limit&. ~NTRODUCTION it is extremely important to obtain information on the simplest chemical reactions such as recombination of atoms. They may play a role in complex mechanisms, which can only be understood if data are available on their rate. On the other hand, they may be accessible to detailed theoretical calculations, especially as to the transfer of energy in collisions. Probably due to experimental difficulties, data are as yet scanty and can in very few cases be used for deciding between different theoretical formulae. Theoretical and experimental results have been discussed comprehensively by 0. I S . Rice (1).Most available data refer to the three-body recombination of bromine (2394) and of iodine atoms (5s6*7).Recently some data have been published on the recombination of chlorine atoms (81QJO). Apparently (9) however, the relatively high value of the dissociation energy of CIS and the low value of the excitation energy (881 cm-1) to the 2P3/2 state of the C1 atom results in experimental difficulties in high temperature experiments, which have not been overcome completely
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