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12 C/ 13 C kinetic isotope effects in the reactions of CH 4 with OH and Cl
Author(s) -
Gupta Mohan L.,
McGrath M. P.,
Cicerone R. J.,
Rowland F. S.,
Wolfsberg M.
Publication year - 1997
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/97gl02858
Subject(s) - kinetic isotope effect , kinetic energy , chemistry , yield (engineering) , isotope , carbon 13 , analytical chemistry (journal) , deuterium , physics , atomic physics , thermodynamics , nuclear physics , environmental chemistry , quantum mechanics
In qualitative agreement with previous MP2 level calculations of the 12 C/ 13 C kinetic isotope effects (KIEs) for H‐abstraction of CH 4 by OH and Cl, higher level calculations yield KIEs at 300 K that differ from the corresponding experimental values, but in different directions. At QCISD(T)/6‐311+G(2df,p), the theoretical KIE for CH 4 +Cl is 32‰ less than the measured value, while for CH 4 +OH, the theoretical KIE is greater than the measured value, but only by 5‰. Noticeable differences in atmospheric model simulation studies can occur if the measured KIEs are replaced by the analogous theoretical values. For example, the effect of carbon isotopic fractionation from the CH 4 + Cl reaction on stratospheric δ 13 CH 4 will be significantly lower than that obtained by Bergamaschi et al. [1996]. It is suggested, for the CH 4 +OH reaction and especially for the CH 4 +Cl reaction, that additional KIE measurements are needed.