Kinetics of Proton Transfer in (H3CH··CH3)-

Document Type


Journal/Book Title

The Journal of Physical Chemistry

Publication Date



American Chemical Society




The rates of proton transfer in (H3CH˙˙CH3)- and its fully deuteriated derivative are calculated by RRKM theory, including contributions from tunneling for energies below the barrier. These results are compared with rates calculated by canonical transition-state theory, incorporating two different tunneling corrections. For temperatures in excess of ca. 500 K, tunneling may be neglected, with all procedures converging on similar transfer rates. However, tunneling plays a progressively larger role as the temperature is lowered, speeding up the transfer by a factor of 30 at 300 K, and completely dominating the reaction below 200 K. The deuterium isotope effect is quite large ( 105) at 0 K, remains fairly constant as the temperature is raised to 50 K, and then drops precipitously from 50 to 500 K, after which it levels off to a high temperature limit of 1.12. The curvature exhibited by an Arrhenius plot below 500 K is unambiguously assigned to tunneling. Adjustment of transition-state theory for tunneling by the Wigner correction is incapable of reproducing the above behavior in the temperature regime where tunneling is important. However, an alternate correction, involving a summation of transmission coefficients, provides an improved recipe for incorporating tunneling into transition-state theory.


Originally published in The Journal of Physical Chemistry by the American Chemical Society . Publisher’s PDF available through remote link. DOI: 10.1021/j100287a046

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