Theoretical study of hot-atom chemistry. the T + HD exchange reactions
Journal of Physical Chemistry , Volume 83 - Issue 8 p. 1033- 1042
The hot-atom exchange reactions T + HD → TH + D and T + HD → TD + H have been studied by trajectory calculations on the Porter-Karplus potential surface up to a laboratory collision energy of 60 eV. The integral reaction probability (IRP) equations for product yields are extended to include the effects of inelastic collisions. The IRP formulas are then reduced to their Monte Carlo form for use with the trajectory calculations. A realistic moderating function P(E,E′) is obtained and resolved into elastic and inelastic contributions. Reactive, nonreactive, and dissociative cross sections are given as a function of energy up to 60 eV. The reaction probabilities are given and reaction mechanisms are discussed. The IRP equations are solved numerically using the realistic and hard-sphere moderating functions to obtain absolute TH and TD product yields and the TH/TD product ratio, and compared to the kinetic theory and experimental results. All three theoretical models agree with the experimental result of 0.70 at 2.8 eV. The realistic IRP model gives an inverted isotope ratio of 1.78 at high energy, whereas the simpler models predict an isotope ratio of 0.80, in much closer agreement with experiment. The differences are related to the detailed shape of P(E,E′) and it is shown that the hard-sphere and kinetic theory models predict the right result by a combination errors. The need for consideration of secondary collisions in a rigorous treatment is emphasized.