The method of Gaussian weighted trajectories. III. An adiabaticity correction proposal

The addition of an adiabaticity correction (AC) to the Gaussian weighted trajectory (GWT) method and its normalized version (GWT-N) is suggested. This correction simply consists in omitting vibrationally adiabatic nonreactive trajectories in the calculations of final attributes. For triatomic exchange reactions, these trajectories satisfy the criterion Omega not much larger than h, where Omega is a vibrational action defined by Omega=integral -infinity infinity dt(pr-p(0)r(0)), r being the reagent diatom bond length, p its conjugate momentum, and r(0) and p(0) the corresponding variables for the unperturbed diatom (Omega/h bears some analogy with the semiclassical elastic scattering phase shift). The resulting GWT-AC and GWT-ACN methods are applied to the recently studied H(+)+H(2) and H(+)+D(2) reactions and the agreement between their predictions and those of exact quantum scattering calculations is found to be much better than for the initial GWT and GWT-N methods. The GWT-AC method, however, appears to be the most accurate one for the processes considered, in particular, the H(+)+D(2) reaction.