Theoretical Research

  During the last fifteen years our theoretical research activity has focused on the study of the dynamics and stereodynamics of elementary bimolecular reactions by means of quasiclassical trajectory (QCT) and time-independent and time-dependent quantum reactive scattering (QM) calculations on highly accurate ab initio potential energy surfaces (PES).

  Our calculations extend from reaction probabilities at zero total angular momentum to state-to-state differential and integral cross sections, excitation functions and thermal rate constants. Our particular interest has been in performing detailed comparisons and simulations of high resolution molecular beam experiments and thermal rate constant data in order to assess the quality of the PES available and of the QCT method in comparison with the more accurate QM methodologies. Elucidating which are the most relevant quantum mechanical effects (tunneling, interferences, resonances, quantum bottlenecks) on the dynamics and stereodynamics of elementary reactions has been the main aim of our research.

  We have concentrated our efforts on 3-atom elementary reactions, such as abstraction reactions (H+H2, F+H2, Cl+H2), insertion reactions (O(1D)+H2, S(1D)+H2, N(2D)+H2, C(1D)+H2) and ion-molecule reactions (H++H2, H++LiH), and more recently, increasing in complexity, on 4-atom (H+H2O and H+N2O) and 6-atom (F+CH4 and Cl+CH4) reactions.

  The stereodynamics of some of these reactions has been studied using QCT and QM methodologies developed in our group. This particular subfield deals with the role of directional factors on reactivity. How the spatial distributions of molecular axes or rotational angular momenta (k-r-k', k-j-k' vector correlations, where k, k' and j, j' are initial and final relative velocities rotational angular momenta, respectively, and r is the direction of the molecular axis) influence the reactivity, and which are the distributions of product angular momentum and their dependence with the scattering angle when the reaction has taken place (kk'j' vector correlation). A rigorous theory in terms of distributions of minimum-uncertainty angular momentum populations to visualize the spatial angular momentum distributions (portraits) leading to reaction has been developed. This method overcomes the limitations of the traditional vector model.

  Inelastic processes have been also treated from both the QCT and QM approaches for systems like H+D2, Ar+NO and He+NO.

  Recently, new QCT strategies have been developed to calculate and analyze the reaction probabilities for any initial rotational angular momentum and cumulative reaction probabilities (CRP) and a statistical model with quasiclassical trajectories (SQCT) has been implemented for insertion reactions.

Dynamics of chemical reactions

  • The hydrogen exchange reaction
  • F+H2 reaction
  • Cl+H2 reaction
  • Insertion reactions
  • Ion-molecule reactions
  • 4- and 6-atom reactions

Stereodynamics of chemical reactions

Ineslastic processes

Cumulative reaction probabilities

Statistical QCT model

Chemical reaction dynamics and femtochemistry