Research work in our group focuses on the theoretical study of the dynamics of elementary chemical reactions. In particular, approximate and exact three-dimensional quantum mechanical methods are used for dealing with triatomic reactions, and quasiclassical methods are used for tetratomic reactions.
In the recent past, both collinear and Reactive-Infinite Order Sudden methods have been used to study reactions such as C + HF --> CH + F, Li + FH --> LiF + H, Li + ClH --> LiCl + H, H + F2 --> HF + F, etc... (for a complete list of the systems dealt with, see published papers). Emphasis was made in the calculation of integral cross sections, differential cross sections, product vibrational distributions, opacity functions and other related quantities and its comparison, whenever possible, with available experimental results, so that deeper insights on the reaction dynamics were obtained.
Our interest moved then to the use of exact methods and developing new procedures. Thus, we have been able to obtain converged cross sections for the Ne + H2+ system by means of the hyperspherical method, as developed by Launay and LeDourneuf. Most noteworthy is the survival of reactive scattering resonances in the integral cross section dependence on collision energy. It indicates that quantum effects for moderately to involved systems are more important than previously predicted.
A new method for doing reactive scattering calculations has been developed. It is based on the use of Negative Imaginary Potentials assembled to an invariant embedding propagation method. This combination allows for an efficient and robust application to triatomic systems. Future work pursues its extension towards polyatomic reactions.
Active collaborations are also in progress with Prof. V. Aquilanti and his group (University of Perugia, Italy), on the implementation of the Hyperquantization Algorithm in reactive scattering, and with Prof. M. Baer and his group (SOREQ NRC, Israel), on the use of NIP-based methods for polyatomic and non-adiabatic processes.
Most recently, a new research line has been opened from a sabbatical stage with the group of Prof. William H. Miller, of the University of California, Berkeley. It is based on developing new semiclassical methods for treating the dynamics of complex molecular systems. New work includes developing the log-derivative version of the prefactor in the Herman-Kluk Initial Value Representation to the semiclassical approximation to the time evolution operator. This formulation has been applied to a model system, a double slit coupled to an ensemble of harmonic oscillators, and shown capable to reproduce both the strong interference pattern in the weak coupling regime and a remarkable decoherence pattern as the coupling or the temperature increases.
Additional work includes the application of the Forward-Backward approximation to study the vibrational relaxation of a diatomic molecule embedded in a bath of harmonic oscillators. It is observed a nice quenching of the excited state as the coupling to the bath or the temperature is increased.
Finally, a new method has been developed for integrating the prefactor in the Herman Kluk IVR SC approach. It is based on implementing a invariant embedding solution to the prefactor's dynamical equations. Results are very encouraging, since an important saving in CPU time is observed (a factor of 300 for a 200 dgree-of-freedom system), while being equally accurate.