A reactant coordinate-based method with a goniometer-shaped grid: higher-order split operators and application to the...

The improved reactant coordinate based method, which could propagate the wave function only using energy-accessible goniometer-shaped grid points, has been proven to be able to crack the coordinate problem for extracting product quantum state-resolved information. In this goniometer-shaped reactant coordinate based (G-RCB) method, the grid points across all three degrees of freedom could be optimally pruned according to the shape of the potential energy surface by a defined cutoff energy; thus, the computational efficiency could be improved significantly. In this work, we demonstrate that, higher order split operators could be safely applied to the G-RCB method as usual, with the cutoff energy only a little higher than the considered energy. With the G-RCB method using higher-order split operators, the reaction between the Cl atom and the vibrationally excited H₂ molecule (v = 1, j = 0) with J = 0 is studied to demonstrate the powerful performance of the method. It was found that, although the vibrationally ground state Cl + H₂ reaction is typically characterized as a simple and direct process, its vibrationally excited reaction requires a very large grid box to obtain accurate numerical results, which involves resonances of exceedingly long distance in the product channel and those over the barrier. With vibrational excitation of the reactant, direct and simple reactions becoming "complex" ones seems inevitable. Thus, the developed G-RCB method should be very promising for studying reactive scattering processes with reactants of vibrational excitations.