Microcanonical variational theory of radical recombination by inversion of interpolated partition function. Isotope effect in CH 3 + H/D

Abstract

Application of the title theory to the recombinations CH 3 + H and CH 3 + D leads to the value of ≈ 2 for the isotope effect. Analysis of this result shows that the increase over the value 2 1 2 expected from simple transition state theory comes almost entirely from the ratio of rotational constants of the doubly degenerate rotation of the symmetric-top CH 3…X (X=H/D) transition state which represents X moving away from CH 3. However the calculated isotope effect remains below the experimental value of ≈ 2.7. Possible reasons for the discrepancy are discussed.