Correlation of Experimental Rate Constants of the Hydrogen Exchange Reactions with a Theoretical H3 Potential Surface, Using Transition-State Theory

Abstract

The recent ab initio potential surface for H₃ obtained by Shavitt, Stevens, Minn, and Karplus is used with one empirical parameter, a uniform scale factor for the energy profile along the reaction path, to compute rate constants for various isotopic forms of the H+H₂ exchange reaction. The scale factor is adjusted to give agreement with the high‐temperature part of the experimental rates recently measured by Westenberg and de Haas, and the results are compared with all the available experimental data. Tunneling is estimated by fitting a one‐dimensional Eckart barrier to the higher 30% of the computed reaction‐path barrier. It is concluded that the ab initio barrier needs to be scaled down by only 11% in order to reproduce the best experimental data, and the “experimental” barrier height is accordingly obtained as 9.8 ± 0.2 kcal/mole.